diff --git a/docs/IMPLEMENTATION_PLAN.md b/docs/IMPLEMENTATION_PLAN.md
index 0544185..befaa06 100644
--- a/docs/IMPLEMENTATION_PLAN.md
+++ b/docs/IMPLEMENTATION_PLAN.md
@@ -1363,3 +1363,20 @@ Worth recording for the next person who reads a gap as a bug: the remaining
 pauses are the market, not the pipe. In thin pre-open tape /ES genuinely goes
 seconds without a price-changing trade, and then moves several ticks at once —
 which is what a "gap up" after a quiet spell actually is.
+
+**The time axis reads local, the data stays UTC.** Lightweight Charts is
+timezone-agnostic: it reads epoch seconds as UTC and labels them as UTC, which
+is why the axis disagreed with the wall clock. Fixed with `tickMarkFormatter`
+for the axis and `localization.timeFormatter` for the crosshair, both going
+through the browser's own zone.
+
+Deliberately *not* fixed by shifting the bar timestamps, which is the other
+common recipe. Every time in this codebase is epoch UTC by convention, and the
+chart's own times feed trendline anchors, `indexAt`, hit testing and the values
+posted back for manual lines — an offset applied to the data would put all of
+them out by the offset, which is exactly the class of bug that once priced a
+trendline 147 points away.
+
+One limit worth knowing: tick *placement* is still computed on UTC days, so the
+day-change divider sits at 00:00 UTC rather than local midnight, labelled with
+the local date. The labels are right; the divider is in the UTC place.
diff --git a/static/chart.js b/static/chart.js
index 6a3ecb9..5f0cf6d 100644
--- a/static/chart.js
+++ b/static/chart.js
@@ -53,7 +53,34 @@ class ConfluenceChart {
         vertLines: { color: 'rgba(128,128,128,.10)' },
         horzLines: { color: 'rgba(128,128,128,.10)' },
       },
-      timeScale: { timeVisible: true, secondsVisible: false },
+      timeScale: {
+        timeVisible: true,
+        secondsVisible: false,
+        // The library is timezone-agnostic: it reads epoch seconds as UTC and
+        // labels them as UTC. Bars stay in UTC — that convention holds
+        // everywhere in this codebase, and shifting the values themselves would
+        // put every trendline anchor, hit test and alert an offset out. Only
+        // the label is localised, via the browser's own zone.
+        tickMarkFormatter: (time, tickMarkType) => {
+          const at = new Date(time * 1000);
+          if (tickMarkType === LightweightCharts.TickMarkType.Year) return String(at.getFullYear());
+          if (tickMarkType === LightweightCharts.TickMarkType.Month) {
+            return at.toLocaleString(undefined, { month: 'short' });
+          }
+          if (tickMarkType === LightweightCharts.TickMarkType.DayOfMonth) return String(at.getDate());
+          return at.toLocaleTimeString(undefined, {
+            hour12: false, hour: '2-digit', minute: '2-digit',
+            ...(tickMarkType === LightweightCharts.TickMarkType.TimeWithSeconds
+              ? { second: '2-digit' } : {}),
+          });
+        },
+      },
+      localization: {
+        // The crosshair readout, which would otherwise disagree with the axis.
+        timeFormatter: time => new Date(time * 1000).toLocaleString(undefined, {
+          hour12: false, month: 'short', day: 'numeric', hour: '2-digit', minute: '2-digit',
+        }),
+      },
       rightPriceScale: { borderVisible: false },
     });
     this.candles = this.chart.addSeries(LightweightCharts.CandlestickSeries, {