diff --git a/frontend/src/components/AnalysisCharts.jsx b/frontend/src/components/AnalysisCharts.jsx
index 7bbc4b6..c1a2738 100644
--- a/frontend/src/components/AnalysisCharts.jsx
+++ b/frontend/src/components/AnalysisCharts.jsx
@@ -1,4 +1,4 @@
-import React, { useState, useMemo } from 'react';
+import React, { useState, useMemo, useEffect } from 'react';
 import { format } from 'date-fns';
 import {
   LineChart, Line, XAxis, YAxis, CartesianGrid, Tooltip,
@@ -7,8 +7,8 @@ import {
 
 // ── Color palettes ─────────────────────────────────────────────────────────────
 
-const CAT_COLORS = { Success: '#22c55e', Failure: '#ef4444', Other: '#9ca3af' };
-const EXTRA_CAT  = ['#f59e0b', '#a855f7', '#ec4899', '#14b8a6', '#f97316'];
+const CAT_COLORS   = { Success: '#22c55e', Failure: '#ef4444', Other: '#9ca3af' };
+const EXTRA_CAT    = ['#f59e0b', '#a855f7', '#ec4899', '#14b8a6', '#f97316'];
 const GROUP_COLORS = ['#6366f1', '#f59e0b', '#22c55e', '#ef4444', '#a855f7', '#14b8a6', '#ec4899', '#f97316', '#84cc16', '#06b6d4'];
 
 function catColor(cat, idx = 0) {
@@ -35,13 +35,14 @@ function ChartTooltip({ active, payload, label, labelKey = 'dateStr', unit = ''
 // ── Shared helpers ─────────────────────────────────────────────────────────────
 
 const DAYS_REACH_RE = /#?\s*days?\s*reach/i;
+const SELECT_CLS    = 'border border-gray-200 rounded px-1.5 py-0.5 text-xs bg-white focus:outline-none focus:ring-1 focus:ring-indigo-400';
+const INPUT_CLS     = 'w-16 border border-gray-200 rounded px-1.5 py-0.5 text-xs bg-white focus:outline-none focus:ring-1 focus:ring-indigo-400';
+const STEP_OPTIONS  = [1, 2, 5, 10];
 
-/** Pick the default xField from a list of active daily-template fields. */
 function defaultXField(fields) {
   return fields.find((f) => DAYS_REACH_RE.test(f.label))?.fieldId ?? '__days__';
 }
 
-/** Read a template field's value from a status row (numeric, or null). */
 function numericFieldVal(status, field) {
   if (!field) return null;
   const raw = field.builtin ? status[field.key] : status.custom_fields?.[field.fieldId];
@@ -49,11 +50,6 @@ function numericFieldVal(status, field) {
   return isNaN(n) ? null : n;
 }
 
-const SELECT_CLS = 'border border-gray-200 rounded px-1.5 py-0.5 text-xs bg-white focus:outline-none focus:ring-1 focus:ring-indigo-400';
-
-const STEP_OPTIONS = [1, 2, 5, 10];
-
-/** Build explicit integer ticks for a numeric x-axis so every step value is shown. */
 function buildTicks(data, step) {
   const xs = data.map((d) => d.x).filter((x) => x != null && isFinite(x));
   if (!xs.length) return undefined;
@@ -83,64 +79,291 @@ function TickStepControl({ value, onChange }) {
   );
 }
 
+// ── Per-chart customisation hook & UI ──────────────────────────────────────────
+
+const HEIGHT_OPTIONS = [
+  { label: 'S', value: 140 },
+  { label: 'M', value: 220 },
+  { label: 'L', value: 340 },
+];
+
+function useChartSettings(defaultHeight) {
+  const [expanded,       setExpanded]       = useState(false);
+  const [height,         setHeight]         = useState(defaultHeight);
+  const [yMin,           setYMin]           = useState('');
+  const [yMax,           setYMax]           = useState('');
+  const [xZoomMin,       setXZoomMin]       = useState('');
+  const [xZoomMax,       setXZoomMax]       = useState('');
+  const [xFieldOverride, setXFieldOverride] = useState(null); // null → use parent's xField
+
+  const yDomain = useMemo(() => [
+    yMin !== '' ? parseFloat(yMin) : 'auto',
+    yMax !== '' ? parseFloat(yMax) : 'auto',
+  ], [yMin, yMax]);
+
+  const xDomain = useMemo(() => {
+    const hasMin = xZoomMin !== '';
+    const hasMax = xZoomMax !== '';
+    if (!hasMin && !hasMax) return null;
+    return [hasMin ? parseFloat(xZoomMin) : 'dataMin', hasMax ? parseFloat(xZoomMax) : 'dataMax'];
+  }, [xZoomMin, xZoomMax]);
+
+  const isDirty = yMin !== '' || yMax !== '' || xZoomMin !== '' || xZoomMax !== ''
+    || xFieldOverride !== null || height !== defaultHeight;
+
+  function reset() {
+    setHeight(defaultHeight);
+    setYMin(''); setYMax('');
+    setXZoomMin(''); setXZoomMax('');
+    setXFieldOverride(null);
+  }
+
+  return {
+    expanded, setExpanded,
+    height, setHeight,
+    yMin, setYMin, yMax, setYMax,
+    xZoomMin, setXZoomMin, xZoomMax, setXZoomMax,
+    xFieldOverride, setXFieldOverride,
+    yDomain, xDomain, isDirty, reset,
+  };
+}
+
+function ChartHeader({ title, isDirty, expanded, onToggle }) {
+  return (
+    <div className="flex items-center justify-between mb-2">
+      <p className="text-xs text-gray-500 font-medium">{title}</p>
+      <button type="button" onClick={onToggle}
+        className={[
+          'text-xs px-2 py-0.5 rounded border transition-colors',
+          expanded
+            ? 'bg-gray-100 border-gray-300 text-gray-700'
+            : isDirty
+              ? 'bg-indigo-50 border-indigo-200 text-indigo-600'
+              : 'bg-white border-gray-200 text-gray-400 hover:text-gray-700 hover:border-gray-300',
+        ].join(' ')}
+      >
+        {expanded ? '▲ collapse' : '▾ customize'}
+      </button>
+    </div>
+  );
+}
+
+// Shown only when the chart card is expanded — renders per-chart controls.
+function ChartSettingsBar({ s, xAxisFields, globalXField, extra }) {
+  return (
+    <div className="mb-3 p-3 bg-gray-50 border border-gray-100 rounded-lg flex flex-wrap gap-x-5 gap-y-2 items-center text-xs">
+
+      {/* Size */}
+      <div className="flex items-center gap-1.5">
+        <span className="text-gray-400 shrink-0">Size:</span>
+        <div className="flex rounded border border-gray-200 overflow-hidden">
+          {HEIGHT_OPTIONS.map((opt) => (
+            <button key={opt.value} type="button" onClick={() => s.setHeight(opt.value)}
+              className={`px-2 py-0.5 transition-colors border-l border-gray-200 first:border-l-0
+                ${s.height === opt.value ? 'bg-gray-700 text-white' : 'bg-white text-gray-500 hover:bg-gray-50'}`}>
+              {opt.label}
+            </button>
+          ))}
+        </div>
+      </div>
+
+      {/* Y range */}
+      <div className="flex items-center gap-1.5">
+        <span className="text-gray-400 shrink-0">Y range:</span>
+        <input type="number" placeholder="min" value={s.yMin} onChange={(e) => s.setYMin(e.target.value)} className={INPUT_CLS} />
+        <span className="text-gray-300">–</span>
+        <input type="number" placeholder="max" value={s.yMax} onChange={(e) => s.setYMax(e.target.value)} className={INPUT_CLS} />
+      </div>
+
+      {/* X zoom */}
+      <div className="flex items-center gap-1.5">
+        <span className="text-gray-400 shrink-0">X zoom:</span>
+        <input type="number" placeholder="min" value={s.xZoomMin} onChange={(e) => s.setXZoomMin(e.target.value)} className={INPUT_CLS} />
+        <span className="text-gray-300">–</span>
+        <input type="number" placeholder="max" value={s.xZoomMax} onChange={(e) => s.setXZoomMax(e.target.value)} className={INPUT_CLS} />
+      </div>
+
+      {/* Per-chart X axis field override */}
+      {xAxisFields.length > 0 && (
+        <div className="flex items-center gap-1.5">
+          <span className="text-gray-400 shrink-0">X data:</span>
+          <select
+            value={s.xFieldOverride ?? globalXField}
+            onChange={(e) => {
+              const v = e.target.value;
+              s.setXFieldOverride(v === globalXField ? null : v);
+            }}
+            className={SELECT_CLS}
+          >
+            <option value="__days__"># Days Reach (ordinal)</option>
+            {xAxisFields.map((f) => <option key={f.fieldId} value={f.fieldId}>{f.label}</option>)}
+          </select>
+        </div>
+      )}
+
+      {/* Slot for chart-specific controls (e.g. Y line visibility) */}
+      {extra}
+
+      {s.isDirty && (
+        <button type="button" onClick={s.reset}
+          className="text-xs text-red-400 hover:text-red-600 transition-colors ml-auto">
+          ↺ Reset
+        </button>
+      )}
+    </div>
+  );
+}
+
+// ── Pure data-computation helpers ──────────────────────────────────────────────
+
+function computeSubjectChartData(xField, statuses, xAxisFields) {
+  const xAxisField = xAxisFields.find((f) => f.fieldId === xField);
+  const xLabel     = xAxisField ? xAxisField.label : '# Days Reach';
+
+  const withMetrics = statuses
+    .filter((s) => s.analysis_summary?.total != null)
+    .sort((a, b) => String(a.date).localeCompare(String(b.date)));
+
+  const rows = withMetrics.map((s, i) => {
+    const xVal    = xField === '__days__' || !xAxisField ? i + 1 : numericFieldVal(s, xAxisField);
+    const dateStr = format(new Date(String(s.date).slice(0, 10) + 'T12:00:00'), 'MMM d');
+    const { counts = {}, total, success_rate } = s.analysis_summary;
+    return { _x: xVal, dateStr, total, rate: success_rate != null ? +(success_rate * 100).toFixed(1) : null, ...counts };
+  }).filter((r) => r._x != null).sort((a, b) => a._x - b._x);
+
+  const data = rows.map((r) => ({ ...r, x: r._x }));
+
+  const catSet = new Set();
+  for (const d of data) {
+    for (const k of Object.keys(d)) {
+      if (!['x', '_x', 'dateStr', 'total', 'rate'].includes(k)) catSet.add(k);
+    }
+  }
+  return { data, cats: [...catSet], xLabel };
+}
+
+function computeExpChartData(xField, chartType, metric, animalRows, lines, xAxisFields) {
+  // chartType: 'count' | 'rate'
+  const xAxisField = xAxisFields.find((f) => f.fieldId === xField);
+  const xLabel     = xAxisField ? xAxisField.label : '# Days Reach';
+
+  function getX(row, dayIndex) {
+    if (xField === '__days__') return dayIndex + 1;
+    return numericFieldVal(row, xAxisField);
+  }
+
+  if (xField === '__days__') {
+    const maxDay = Math.max(0, ...lines.map((l) => animalRows[l.id].length));
+    if (maxDay === 0) return { data: [], xLabel };
+    const data = Array.from({ length: maxDay }, (_, i) => ({ x: i + 1 }));
+    for (const line of lines) {
+      animalRows[line.id].forEach((row, i) => {
+        const s = row.analysis_summary;
+        if (chartType === 'count') {
+          data[i][line.id] = metric === 'total' ? s.total : (s.counts?.[metric] ?? null);
+        } else {
+          data[i][line.id] = s.success_rate != null ? +(s.success_rate * 100).toFixed(1) : null;
+        }
+      });
+    }
+    return { data, xLabel };
+  }
+
+  // Field-based x axis
+  const allPts = [];
+  for (const line of lines) {
+    animalRows[line.id].forEach((row, i) => {
+      const x = getX(row, i);
+      if (x !== null) allPts.push({ x, animalId: line.id, summary: row.analysis_summary });
+    });
+  }
+  const sortedX = [...new Set(allPts.map((p) => p.x))].sort((a, b) => a - b);
+  if (sortedX.length === 0) return { data: [], xLabel };
+
+  const data = sortedX.map((x) => {
+    const pt = { x };
+    for (const p of allPts.filter((pp) => pp.x === x)) {
+      const s = p.summary;
+      if (chartType === 'count') {
+        pt[p.animalId] = metric === 'total' ? s.total : (s.counts?.[metric] ?? null);
+      } else {
+        pt[p.animalId] = s.success_rate != null ? +(s.success_rate * 100).toFixed(1) : null;
+      }
+    }
+    return pt;
+  });
+  return { data, xLabel };
+}
+
 // ── Subject charts ─────────────────────────────────────────────────────────────
 
 export function SubjectAnalysisCharts({ statuses, dailyTemplate }) {
-  const xAxisFields = (dailyTemplate ?? []).filter((f) => f.active);
-  const [xField, setXField] = useState(() => defaultXField(xAxisFields));
-  const [tickStep, setTickStep] = useState(1);
+  const xAxisFields = useMemo(
+    () => (dailyTemplate ?? []).filter((f) => f.active),
+    [dailyTemplate],
+  );
+  const [xField,    setXField]    = useState(() => defaultXField(xAxisFields));
+  const [tickStep,  setTickStep]  = useState(1);
 
-  const { data, cats, xLabel } = useMemo(() => {
-    const xAxisField = xAxisFields.find((f) => f.fieldId === xField);
-    const xLabel = xAxisField ? xAxisField.label : '# Days Reach';
+  const countsS = useChartSettings(200);
+  const rateS   = useChartSettings(160);
 
-    const withMetrics = statuses
-      .filter((s) => s.analysis_summary?.total != null)
-      .sort((a, b) => String(a.date).localeCompare(String(b.date)));
+  // Shared base computation — used by both charts when no override is set
+  const sharedData = useMemo(
+    () => computeSubjectChartData(xField, statuses, xAxisFields),
+    [xField, statuses, xAxisFields],
+  );
 
-    const rows = withMetrics.map((s, i) => {
-      const xVal = xField === '__days__' || !xAxisField
-        ? i + 1
-        : numericFieldVal(s, xAxisField);
-      const dateStr = format(new Date(String(s.date).slice(0, 10) + 'T12:00:00'), 'MMM d');
-      const { counts = {}, total, success_rate } = s.analysis_summary;
-      return { _x: xVal, dateStr, total, rate: success_rate != null ? +(success_rate * 100).toFixed(1) : null, ...counts };
-    }).filter((r) => r._x != null).sort((a, b) => a._x - b._x);
+  // Per-chart overrides: only recompute when the override differs from the shared field
+  const countsData = useMemo(() => {
+    const ef = countsS.xFieldOverride;
+    if (!ef || ef === xField) return sharedData;
+    return computeSubjectChartData(ef, statuses, xAxisFields);
+  }, [countsS.xFieldOverride, xField, sharedData, statuses, xAxisFields]);
 
-    const data = rows.map((r) => ({ ...r, x: r._x }));
+  const rateData = useMemo(() => {
+    const ef = rateS.xFieldOverride;
+    if (!ef || ef === xField) return sharedData;
+    return computeSubjectChartData(ef, statuses, xAxisFields);
+  }, [rateS.xFieldOverride, xField, sharedData, statuses, xAxisFields]);
 
-    const catSet = new Set();
-    for (const d of data) {
-      for (const k of Object.keys(d)) {
-        if (!['x', '_x', 'dateStr', 'total', 'rate'].includes(k)) catSet.add(k);
-      }
-    }
-    return { data, cats: [...catSet], xLabel };
-  }, [statuses, xField, dailyTemplate]);
+  const countsTicks = useMemo(() => buildTicks(countsData.data, tickStep), [countsData.data, tickStep]);
+  const rateTicks   = useMemo(() => buildTicks(rateData.data,   tickStep), [rateData.data,   tickStep]);
 
-  const ticks = useMemo(() => buildTicks(data, tickStep), [data, tickStep]);
+  // Y-line visibility for the counts chart (null = show all)
+  const [visibleCats, setVisibleCats] = useState(null);
+  useEffect(() => { setVisibleCats(null); }, [countsData.cats.join(',')]); // reset when cats change
 
-  if (data.length === 0) return null;
+  if (sharedData.data.length === 0) return null;
 
-  const xAxisProps = {
-    dataKey: 'x', type: 'number', tick: { fontSize: 10 },
-    ticks,
-    domain: ticks?.length ? [ticks[0], ticks[ticks.length - 1]] : ['auto', 'auto'],
-    label: { value: xLabel, position: 'insideBottomRight', offset: -4, fontSize: 10 },
-    allowDecimals: false,
-  };
+  function toggleCat(cat) {
+    setVisibleCats((prev) => {
+      if (prev === null) return new Set([cat]);
+      const next = new Set(prev);
+      next.has(cat) ? next.delete(cat) : next.add(cat);
+      return next.size === 0 ? null : next;
+    });
+  }
+
+  function xAxisProps(data, ticks, s) {
+    const ef         = s.xFieldOverride ?? xField;
+    const xAxisField = xAxisFields.find((f) => f.fieldId === ef);
+    const xLabel     = xAxisField ? xAxisField.label : '# Days Reach';
+    const domain     = s.xDomain ?? (ticks?.length ? [ticks[0], ticks[ticks.length - 1]] : ['auto', 'auto']);
+    return { dataKey: 'x', type: 'number', tick: { fontSize: 10 }, ticks, domain, allowDecimals: false,
+      label: { value: xLabel, position: 'insideBottomRight', offset: -4, fontSize: 10 } };
+  }
 
   return (
     <div className="bg-white border border-gray-200 rounded-xl p-5 mb-6 space-y-5">
+      {/* Global controls */}
       <div className="flex items-center flex-wrap gap-3">
         <h2 className="text-sm font-semibold text-gray-700 uppercase tracking-wide">Session metrics over time</h2>
         <div className="flex items-center gap-1.5 text-xs">
           <span className="text-gray-400">X axis:</span>
           <select value={xField} onChange={(e) => setXField(e.target.value)} className={SELECT_CLS}>
             <option value="__days__"># Days Reach (ordinal)</option>
-            {xAxisFields.map((f) => (
-              <option key={f.fieldId} value={f.fieldId}>{f.label}</option>
-            ))}
+            {xAxisFields.map((f) => <option key={f.fieldId} value={f.fieldId}>{f.label}</option>)}
           </select>
         </div>
         <TickStepControl value={tickStep} onChange={setTickStep} />
@@ -148,32 +371,63 @@ export function SubjectAnalysisCharts({ statuses, dailyTemplate }) {
 
       {/* Chart 1 — counts */}
       <div>
-        <p className="text-xs text-gray-500 mb-2">Attempts per session</p>
-        <ResponsiveContainer width="100%" height={200}>
-          <LineChart data={data} margin={{ top: 4, right: 16, left: 0, bottom: 4 }}>
+        <ChartHeader title="Attempts per session" isDirty={countsS.isDirty} expanded={countsS.expanded} onToggle={() => countsS.setExpanded((e) => !e)} />
+        {countsS.expanded && (
+          <ChartSettingsBar s={countsS} xAxisFields={xAxisFields} globalXField={xField}
+            extra={
+              countsData.cats.length > 0 && (
+                <div className="flex items-center gap-2 flex-wrap">
+                  <span className="text-gray-400 shrink-0">Y lines:</span>
+                  {countsData.cats.map((cat, i) => {
+                    const on = visibleCats === null || visibleCats.has(cat);
+                    return (
+                      <button key={cat} type="button" onClick={() => toggleCat(cat)}
+                        style={{ color: catColor(cat, i), borderColor: on ? catColor(cat, i) : '#e5e7eb' }}
+                        className={`px-2 py-0.5 rounded border text-xs transition-opacity ${on ? 'opacity-100' : 'opacity-35'}`}>
+                        {cat}
+                      </button>
+                    );
+                  })}
+                </div>
+              )
+            }
+          />
+        )}
+        <ResponsiveContainer width="100%" height={countsS.height}>
+          <LineChart data={countsData.data} margin={{ top: 4, right: 16, left: 0, bottom: 4 }}>
             <CartesianGrid strokeDasharray="3 3" stroke="#f3f4f6" />
-            <XAxis {...xAxisProps} />
-            <YAxis tick={{ fontSize: 10 }} width={30} allowDecimals={false} />
+            <XAxis {...xAxisProps(countsData.data, countsTicks, countsS)} />
+            <YAxis tick={{ fontSize: 10 }} width={30} allowDecimals={false} domain={countsS.yDomain} />
             <Tooltip content={<ChartTooltip labelKey="dateStr" />} />
             <Legend wrapperStyle={{ fontSize: 11 }} />
-            {cats.map((cat, i) => (
-              <Line key={cat} type="monotone" dataKey={cat} stroke={catColor(cat, i)} strokeWidth={2} dot={{ r: 3 }} activeDot={{ r: 4 }} connectNulls isAnimationActive={false} />
-            ))}
-            <Line type="monotone" dataKey="total" name="Total" stroke="#3b82f6" strokeWidth={1.5} strokeDasharray="5 3" dot={{ r: 3 }} connectNulls isAnimationActive={false} />
+            {countsData.cats
+              .filter((cat) => visibleCats === null || visibleCats.has(cat))
+              .map((cat, i) => (
+                <Line key={cat} type="monotone" dataKey={cat} stroke={catColor(cat, i)} strokeWidth={2}
+                  dot={{ r: 3 }} activeDot={{ r: 4 }} connectNulls isAnimationActive={false} />
+              ))}
+            <Line type="monotone" dataKey="total" name="Total" stroke="#3b82f6" strokeWidth={1.5}
+              strokeDasharray="5 3" dot={{ r: 3 }} connectNulls isAnimationActive={false} />
           </LineChart>
         </ResponsiveContainer>
       </div>
 
       {/* Chart 2 — success rate */}
       <div>
-        <p className="text-xs text-gray-500 mb-2">Success rate (%)</p>
-        <ResponsiveContainer width="100%" height={160}>
-          <LineChart data={data} margin={{ top: 4, right: 16, left: 0, bottom: 4 }}>
+        <ChartHeader title="Success rate (%)" isDirty={rateS.isDirty} expanded={rateS.expanded} onToggle={() => rateS.setExpanded((e) => !e)} />
+        {rateS.expanded && (
+          <ChartSettingsBar s={rateS} xAxisFields={xAxisFields} globalXField={xField} />
+        )}
+        <ResponsiveContainer width="100%" height={rateS.height}>
+          <LineChart data={rateData.data} margin={{ top: 4, right: 16, left: 0, bottom: 4 }}>
             <CartesianGrid strokeDasharray="3 3" stroke="#f3f4f6" />
-            <XAxis {...xAxisProps} />
-            <YAxis tick={{ fontSize: 10 }} width={36} domain={[0, 100]} tickFormatter={(v) => `${v}%`} />
+            <XAxis {...xAxisProps(rateData.data, rateTicks, rateS)} />
+            <YAxis tick={{ fontSize: 10 }} width={36}
+              domain={rateS.yDomain[0] !== 'auto' || rateS.yDomain[1] !== 'auto' ? rateS.yDomain : [0, 100]}
+              tickFormatter={(v) => `${v}%`} />
             <Tooltip content={<ChartTooltip unit="%" labelKey="dateStr" />} />
-            <Line type="monotone" dataKey="rate" name="Success rate" stroke="#6366f1" strokeWidth={2} dot={{ r: 3 }} connectNulls isAnimationActive={false} />
+            <Line type="monotone" dataKey="rate" name="Success rate" stroke="#6366f1" strokeWidth={2}
+              dot={{ r: 3 }} connectNulls isAnimationActive={false} />
           </LineChart>
         </ResponsiveContainer>
       </div>
@@ -190,17 +444,20 @@ const METRIC_OPTIONS = [
 ];
 
 export function ExperimentAnalysisCharts({ animals, experimentStatuses, subjectTemplate, dailyTemplate }) {
-  const groupableFields  = (subjectTemplate ?? []).filter((f) => f.active);
-  const xAxisFields      = (dailyTemplate    ?? []).filter((f) => f.active);
+  const groupableFields = useMemo(() => (subjectTemplate ?? []).filter((f) => f.active), [subjectTemplate]);
+  const xAxisFields     = useMemo(() => (dailyTemplate    ?? []).filter((f) => f.active), [dailyTemplate]);
 
   const defaultGroup = (groupableFields.find((f) => /^group$/i.test(f.label)) ?? groupableFields[0])?.fieldId ?? '';
-  const [groupBy,   setGroupBy]   = useState(defaultGroup);
-  const [metric,    setMetric]    = useState('total');
-  const [xField,    setXField]    = useState(() => defaultXField(xAxisFields));
-  const [tickStep,  setTickStep]  = useState(1);
+  const [groupBy,  setGroupBy]  = useState(defaultGroup);
+  const [metric,   setMetric]   = useState('total');
+  const [xField,   setXField]   = useState(() => defaultXField(xAxisFields));
+  const [tickStep, setTickStep] = useState(1);
 
-  const { countData, rateData, lines, xLabel } = useMemo(() => {
-    // animalId → group label
+  const countsS = useChartSettings(200);
+  const rateS   = useChartSettings(160);
+
+  // Step 1: animalRows — does NOT depend on xField; shared by both charts
+  const { animalRows, lines } = useMemo(() => {
     const animalGroup = {};
     for (const animal of animals) {
       const raw = groupBy ? animal.subject_info?.[groupBy] : null;
@@ -208,13 +465,12 @@ export function ExperimentAnalysisCharts({ animals, experimentStatuses, subjectT
     }
     const groups = [...new Set(Object.values(animalGroup))].sort();
 
-    // animalId → sorted statuses that have saved metrics (full status rows)
     const statusesByAnimal = {};
     for (const s of experimentStatuses) {
       if (!statusesByAnimal[s.animal_id]) statusesByAnimal[s.animal_id] = [];
       statusesByAnimal[s.animal_id].push(s);
     }
-    const animalRows = {};   // full status rows, sorted by date
+    const animalRows = {};
     for (const animal of animals) {
       animalRows[animal.id] = (statusesByAnimal[animal.id] ?? [])
         .filter((s) => s.analysis_summary?.total != null)
@@ -222,7 +478,7 @@ export function ExperimentAnalysisCharts({ animals, experimentStatuses, subjectT
     }
 
     const lines = animals
-      .filter((a) => animalRows[a.id].length > 0)
+      .filter((a) => animalRows[a.id]?.length > 0)
       .map((a) => ({
         id:    a.id,
         name:  a.animal_name,
@@ -230,85 +486,40 @@ export function ExperimentAnalysisCharts({ animals, experimentStatuses, subjectT
         color: GROUP_COLORS[groups.indexOf(animalGroup[a.id]) % GROUP_COLORS.length],
       }));
 
-    if (lines.length === 0) return { countData: [], rateData: [], lines: [], xLabel: '' };
+    return { animalRows, lines };
+  }, [animals, experimentStatuses, groupBy]);
 
-    const xAxisField = xAxisFields.find((f) => f.fieldId === xField);
-    const xLabel     = xAxisField ? xAxisField.label : '# Days Reach';
+  // Step 2: count chart data — depends on xField for counts + metric
+  const { data: countData, xLabel: countsXLabel } = useMemo(() => {
+    if (lines.length === 0) return { data: [], xLabel: '' };
+    const ef = countsS.xFieldOverride ?? xField;
+    return computeExpChartData(ef, 'count', metric, animalRows, lines, xAxisFields);
+  }, [animalRows, lines, countsS.xFieldOverride, xField, metric, xAxisFields]);
 
-    function getX(row, dayIndex) {
-      if (xField === '__days__') return dayIndex + 1;
-      return numericFieldVal(row, xAxisField);
-    }
+  // Step 3: rate chart data — depends on xField for rate
+  const { data: rateData, xLabel: rateXLabel } = useMemo(() => {
+    if (lines.length === 0) return { data: [], xLabel: '' };
+    const ef = rateS.xFieldOverride ?? xField;
+    return computeExpChartData(ef, 'rate', null, animalRows, lines, xAxisFields);
+  }, [animalRows, lines, rateS.xFieldOverride, xField, xAxisFields]);
 
-    function getCountVal(summary) {
-      return metric === 'total'
-        ? summary.total
-        : (summary.counts?.[metric] ?? null);
-    }
-
-    if (xField === '__days__') {
-      // Ordinal alignment: position by day index
-      const maxDay = Math.max(...lines.map((l) => animalRows[l.id].length));
-      const countData = Array.from({ length: maxDay }, (_, i) => ({ x: i + 1 }));
-      const rateData  = Array.from({ length: maxDay }, (_, i) => ({ x: i + 1 }));
-      for (const line of lines) {
-        animalRows[line.id].forEach((row, i) => {
-          const s = row.analysis_summary;
-          countData[i][line.id] = getCountVal(s);
-          rateData[i][line.id]  = s.success_rate != null ? +(s.success_rate * 100).toFixed(1) : null;
-        });
-      }
-      return { countData, rateData, lines, xLabel };
-    }
-
-    // Field-based x axis: merge all unique x values across animals
-    const allPts = [];
-    for (const line of lines) {
-      animalRows[line.id].forEach((row, i) => {
-        const x = getX(row, i);
-        if (x !== null) allPts.push({ x, animalId: line.id, summary: row.analysis_summary });
-      });
-    }
-    const sortedX = [...new Set(allPts.map((p) => p.x))].sort((a, b) => a - b);
-    if (sortedX.length === 0) return { countData: [], rateData: [], lines, xLabel };
-
-    const countData = sortedX.map((x) => {
-      const pt = { x };
-      for (const p of allPts.filter((p) => p.x === x)) {
-        pt[p.animalId] = getCountVal(p.summary);
-      }
-      return pt;
-    });
-    const rateData = sortedX.map((x) => {
-      const pt = { x };
-      for (const p of allPts.filter((p) => p.x === x)) {
-        const s = p.summary;
-        pt[p.animalId] = s.success_rate != null ? +(s.success_rate * 100).toFixed(1) : null;
-      }
-      return pt;
-    });
-
-    return { countData, rateData, lines, xLabel };
-  }, [animals, experimentStatuses, subjectTemplate, dailyTemplate, groupBy, metric, xField]);
+  const countsTicks = useMemo(() => buildTicks(countData, tickStep), [countData, tickStep]);
+  const rateTicks   = useMemo(() => buildTicks(rateData,  tickStep), [rateData,  tickStep]);
 
   const hasData = lines.length > 0;
-  const countTicks = useMemo(() => buildTicks(countData, tickStep), [countData, tickStep]);
-  const rateTicks  = useMemo(() => buildTicks(rateData,  tickStep), [rateData,  tickStep]);
 
-  function xAxisProps(ticks) {
-    return {
-      dataKey: 'x', type: 'number', tick: { fontSize: 10 }, allowDecimals: false,
-      ticks,
-      domain: ticks?.length ? [ticks[0], ticks[ticks.length - 1]] : ['auto', 'auto'],
-      label: { value: xLabel, position: 'insideBottomRight', offset: -4, fontSize: 10 },
-    };
+  function xAxisProps(data, ticks, s, fallbackLabel) {
+    const domain = s.xDomain ?? (ticks?.length ? [ticks[0], ticks[ticks.length - 1]] : ['auto', 'auto']);
+    const label  = (s.xFieldOverride ? xAxisFields.find((f) => f.fieldId === s.xFieldOverride)?.label : null) ?? fallbackLabel;
+    return { dataKey: 'x', type: 'number', tick: { fontSize: 10 }, ticks, domain, allowDecimals: false,
+      label: { value: label, position: 'insideBottomRight', offset: -4, fontSize: 10 } };
   }
 
   function ExpTooltip({ active, payload, label, unit = '' }) {
     if (!active || !payload?.length) return null;
     return (
       <div className="bg-white border border-gray-200 rounded shadow-sm px-3 py-2 text-xs space-y-0.5 max-h-48 overflow-y-auto">
-        <p className="font-semibold text-gray-700 mb-1">{xLabel}: {label}</p>
+        <p className="font-semibold text-gray-700 mb-1">{label}</p>
         {payload.map((p) => {
           const line = lines.find((l) => l.id === p.dataKey);
           return p.value != null ? (
@@ -323,29 +534,22 @@ export function ExperimentAnalysisCharts({ animals, experimentStatuses, subjectT
 
   return (
     <div className="bg-white border border-gray-200 rounded-xl p-5 mb-6 space-y-5">
+      {/* Global controls */}
       <div className="flex items-center flex-wrap gap-3">
         <h2 className="text-sm font-semibold text-gray-700 uppercase tracking-wide">Cross-subject metrics</h2>
-
-        {/* X-axis field selector */}
         <div className="flex items-center gap-1.5 text-xs">
           <span className="text-gray-400">X axis:</span>
           <select value={xField} onChange={(e) => setXField(e.target.value)} className={SELECT_CLS}>
             <option value="__days__"># Days Reach (ordinal)</option>
-            {xAxisFields.map((f) => (
-              <option key={f.fieldId} value={f.fieldId}>{f.label}</option>
-            ))}
+            {xAxisFields.map((f) => <option key={f.fieldId} value={f.fieldId}>{f.label}</option>)}
           </select>
         </div>
-
-        {/* Color-by subject info field */}
         {groupableFields.length > 0 && (
           <div className="flex items-center gap-1.5 text-xs">
             <span className="text-gray-400">Color by:</span>
             <select value={groupBy} onChange={(e) => setGroupBy(e.target.value)} className={SELECT_CLS}>
               <option value="">— none —</option>
-              {groupableFields.map((f) => (
-                <option key={f.fieldId} value={f.fieldId}>{f.label}</option>
-              ))}
+              {groupableFields.map((f) => <option key={f.fieldId} value={f.fieldId}>{f.label}</option>)}
             </select>
           </div>
         )}
@@ -353,36 +557,54 @@ export function ExperimentAnalysisCharts({ animals, experimentStatuses, subjectT
       </div>
 
       {!hasData && (
-        <p className="text-sm text-gray-400 italic">No sessions with saved metrics yet. Upload a CSV on a daily status page and click "Save metrics to daily status".</p>
+        <p className="text-sm text-gray-400 italic">No sessions with saved metrics yet.</p>
       )}
 
       {hasData && (
         <>
           {/* Chart 1 — counts */}
           <div>
-            <div className="flex items-center gap-3 mb-2">
-              <p className="text-xs text-gray-500">Count per session — each line is one subject</p>
-              <div className="flex rounded border border-gray-200 overflow-hidden text-[10px]">
-                {METRIC_OPTIONS.map((opt) => (
-                  <button key={opt.value} type="button" onClick={() => setMetric(opt.value)}
-                    className={`px-2 py-0.5 transition-colors border-l border-gray-200 first:border-l-0
-                      ${metric === opt.value ? 'bg-gray-700 text-white' : 'bg-white text-gray-500 hover:bg-gray-50'}`}>
-                    {opt.label}
-                  </button>
-                ))}
+            <div className="flex items-center justify-between mb-2 flex-wrap gap-2">
+              <div className="flex items-center gap-3">
+                <p className="text-xs text-gray-500 font-medium">Count per session</p>
+                {/* Y-metric selector stays at chart level — primary control */}
+                <div className="flex rounded border border-gray-200 overflow-hidden text-[10px]">
+                  {METRIC_OPTIONS.map((opt) => (
+                    <button key={opt.value} type="button" onClick={() => setMetric(opt.value)}
+                      className={`px-2 py-0.5 transition-colors border-l border-gray-200 first:border-l-0
+                        ${metric === opt.value ? 'bg-gray-700 text-white' : 'bg-white text-gray-500 hover:bg-gray-50'}`}>
+                      {opt.label}
+                    </button>
+                  ))}
+                </div>
               </div>
+              <button type="button" onClick={() => countsS.setExpanded((e) => !e)}
+                className={[
+                  'text-xs px-2 py-0.5 rounded border transition-colors',
+                  countsS.expanded
+                    ? 'bg-gray-100 border-gray-300 text-gray-700'
+                    : countsS.isDirty
+                      ? 'bg-indigo-50 border-indigo-200 text-indigo-600'
+                      : 'bg-white border-gray-200 text-gray-400 hover:text-gray-700 hover:border-gray-300',
+                ].join(' ')}>
+                {countsS.expanded ? '▲ collapse' : '▾ customize'}
+              </button>
             </div>
-            <ResponsiveContainer width="100%" height={200}>
+            {countsS.expanded && (
+              <ChartSettingsBar s={countsS} xAxisFields={xAxisFields} globalXField={xField} />
+            )}
+            <ResponsiveContainer width="100%" height={countsS.height}>
               <LineChart data={countData} margin={{ top: 4, right: 16, left: 0, bottom: 4 }}>
                 <CartesianGrid strokeDasharray="3 3" stroke="#f3f4f6" />
-                <XAxis {...xAxisProps(countTicks)} />
-                <YAxis tick={{ fontSize: 10 }} width={30} allowDecimals={false} />
+                <XAxis {...xAxisProps(countData, countsTicks, countsS, countsXLabel)} />
+                <YAxis tick={{ fontSize: 10 }} width={30} allowDecimals={false} domain={countsS.yDomain} />
                 <Tooltip content={<ExpTooltip />} />
                 <Legend wrapperStyle={{ fontSize: 11 }}
                   formatter={(value) => lines.find((l) => l.id === value)?.name ?? value} />
                 {lines.map((l) => (
                   <Line key={l.id} type="monotone" dataKey={l.id} name={l.id}
-                    stroke={l.color} strokeWidth={2} dot={{ r: 3 }} activeDot={{ r: 5 }} connectNulls isAnimationActive={false} />
+                    stroke={l.color} strokeWidth={2} dot={{ r: 3 }} activeDot={{ r: 5 }}
+                    connectNulls isAnimationActive={false} />
                 ))}
               </LineChart>
             </ResponsiveContainer>
@@ -390,18 +612,24 @@ export function ExperimentAnalysisCharts({ animals, experimentStatuses, subjectT
 
           {/* Chart 2 — success rate */}
           <div>
-            <p className="text-xs text-gray-500 mb-2">Success rate (%) — each line is one subject</p>
-            <ResponsiveContainer width="100%" height={160}>
+            <ChartHeader title="Success rate (%) — each line is one subject" isDirty={rateS.isDirty} expanded={rateS.expanded} onToggle={() => rateS.setExpanded((e) => !e)} />
+            {rateS.expanded && (
+              <ChartSettingsBar s={rateS} xAxisFields={xAxisFields} globalXField={xField} />
+            )}
+            <ResponsiveContainer width="100%" height={rateS.height}>
               <LineChart data={rateData} margin={{ top: 4, right: 16, left: 0, bottom: 4 }}>
                 <CartesianGrid strokeDasharray="3 3" stroke="#f3f4f6" />
-                <XAxis {...xAxisProps(rateTicks)} />
-                <YAxis tick={{ fontSize: 10 }} width={36} domain={[0, 100]} tickFormatter={(v) => `${v}%`} />
+                <XAxis {...xAxisProps(rateData, rateTicks, rateS, rateXLabel)} />
+                <YAxis tick={{ fontSize: 10 }} width={36}
+                  domain={rateS.yDomain[0] !== 'auto' || rateS.yDomain[1] !== 'auto' ? rateS.yDomain : [0, 100]}
+                  tickFormatter={(v) => `${v}%`} />
                 <Tooltip content={<ExpTooltip unit="%" />} />
                 <Legend wrapperStyle={{ fontSize: 11 }}
                   formatter={(value) => lines.find((l) => l.id === value)?.name ?? value} />
                 {lines.map((l) => (
                   <Line key={l.id} type="monotone" dataKey={l.id} name={l.id}
-                    stroke={l.color} strokeWidth={2} dot={{ r: 3 }} activeDot={{ r: 5 }} connectNulls isAnimationActive={false} />
+                    stroke={l.color} strokeWidth={2} dot={{ r: 3 }} activeDot={{ r: 5 }}
+                    connectNulls isAnimationActive={false} />
                 ))}
               </LineChart>
             </ResponsiveContainer>