diff --git a/JoshHeaps.Net/wwwroot/js/casino/holdem/actionBar.js b/JoshHeaps.Net/wwwroot/js/casino/holdem/actionBar.js
index 1998e6e..0e5d969 100644
--- a/JoshHeaps.Net/wwwroot/js/casino/holdem/actionBar.js
+++ b/JoshHeaps.Net/wwwroot/js/casino/holdem/actionBar.js
@@ -11,6 +11,11 @@ const ActionBar = {
     mount(state, hooks) {
         this.state = state;
         this.hooks = hooks;
+        // Whoever was already on the clock when this page loaded — see tankUnknownFor.
+        this.tankUnknownFor = state.bettingOpen &&
+            state.actingSeatIndex !== null && state.actingSeatIndex !== undefined
+            ? state.actingSeatIndex
+            : null;
         this.watchHeight();
         this.render();
     },
@@ -207,6 +212,14 @@ const ActionBar = {
     tankStartedAt: null,
     tankInterval: null,
 
+    // The seat that was already being asked to act when this page loaded, if there was
+    // one. Its clock is unknowable: the action moved to them before this session
+    // started — maybe two minutes ago, maybe last night — and starting from zero would
+    // have the bar say they had just begun thinking. Which it did, every time a dealer
+    // refreshed mid-hand. Cleared the moment the action moves, because from then on the
+    // clock is measuring something it actually saw.
+    tankUnknownFor: null,
+
     // Restarts only when the action actually moves — a re-render for any other reason
     // (a chip edit, a name change) must not put a thinking player back to zero.
     syncTankTimer() {
@@ -220,6 +233,8 @@ const ActionBar = {
         }
 
         if (this.tankSeatIndex !== index) {
+            // Once the action has moved under our own eyes, nothing is unknown any more.
+            if (this.tankSeatIndex !== null) this.tankUnknownFor = null;
             this.tankSeatIndex = index;
             this.tankStartedAt = Date.now();
         }
@@ -243,13 +258,33 @@ const ActionBar = {
         const el = document.getElementById("actionTank");
         if (!el || this.tankStartedAt === null) return;
 
+        if (this.tankUnknownFor !== null && this.tankSeatIndex === this.tankUnknownFor) {
+            el.textContent = "—";
+            el.title = "The action was already on this seat when the page loaded, so there's nothing to time from yet. The clock starts when the action next moves.";
+            el.classList.remove("tankNudge", "tankSlow");
+            return;
+        }
+
         const seconds = Math.floor((Date.now() - this.tankStartedAt) / 1000);
-        const mins = Math.floor(seconds / 60);
-        el.textContent = `${mins}:${String(seconds % 60).padStart(2, "0")}`;
+        el.title = "How long this player has been thinking";
+        el.textContent = this.formatTank(seconds);
         el.classList.toggle("tankNudge", seconds >= this.NUDGE_AFTER_S && seconds < this.SLOW_AFTER_S);
         el.classList.toggle("tankSlow", seconds >= this.SLOW_AFTER_S);
     },
 
+    // "0:07", "4:01", and past the hour "1:05:03" rather than "65:03" — a table left
+    // open on a hand does reach that, and sixty-five minutes written as though it were
+    // a minutes-and-seconds reading is a number the eye gets wrong.
+    formatTank(seconds) {
+        const pad = value => String(value).padStart(2, "0");
+        const hours = Math.floor(seconds / 3600);
+        const minutes = Math.floor((seconds % 3600) / 60);
+        const rest = seconds % 60;
+        return hours > 0
+            ? `${hours}:${pad(minutes)}:${pad(rest)}`
+            : `${minutes}:${pad(rest)}`;
+    },
+
     // Shown only once someone is all-in and the money has actually split — a single
     // undivided pot needs no announcement, and a line that's always there stops being
     // read.
diff --git a/tests/holdem/tankClock.test.js b/tests/holdem/tankClock.test.js
new file mode 100644
index 0000000..1dccacf
--- /dev/null
+++ b/tests/holdem/tankClock.test.js
@@ -0,0 +1,37 @@
+// How the think-clock reads.
+const test = require("node:test");
+const assert = require("node:assert");
+const path = require("path");
+
+const ActionBar = require(path.join(
+    __dirname, "..", "..", "JoshHeaps.Net", "wwwroot", "js", "casino", "holdem", "actionBar.js"));
+
+test("seconds under a minute", () => {
+    assert.equal(ActionBar.formatTank(0), "0:00");
+    assert.equal(ActionBar.formatTank(7), "0:07");
+    assert.equal(ActionBar.formatTank(59), "0:59");
+});
+
+test("minutes and seconds", () => {
+    assert.equal(ActionBar.formatTank(60), "1:00");
+    assert.equal(ActionBar.formatTank(241), "4:01");
+    assert.equal(ActionBar.formatTank(3599), "59:59");
+});
+
+test("past the hour it says the hour", () => {
+    // A table left open on a hand reaches this, and "65:03" is a number the eye reads
+    // as minutes and seconds when it isn't.
+    assert.equal(ActionBar.formatTank(3600), "1:00:00");
+    assert.equal(ActionBar.formatTank(3903), "1:05:03");
+    assert.equal(ActionBar.formatTank(45296), "12:34:56");
+});
+
+test("the minutes are padded once there are hours, and not before", () => {
+    // "1:5:03" would be wrong; "05:03" on its own would be odd.
+    assert.equal(ActionBar.formatTank(3903), "1:05:03");
+    assert.equal(ActionBar.formatTank(303), "5:03");
+});
+
+test("a day is still a readable number rather than a wrapped one", () => {
+    assert.equal(ActionBar.formatTank(90000), "25:00:00");
+});