diff --git a/docs/preset_test.md b/docs/preset_test.md
index bd6cfa0c..5f309c83 100644
--- a/docs/preset_test.md
+++ b/docs/preset_test.md
@@ -108,8 +108,9 @@ Open a generated URL to see that test's status, instructions, and commands.
       <p class="preset-test-note">
         This changes only the absolute <code>tempradioat</code> and
         <code>tempradioat2</code> epochs shown on this page; it does not issue a
-        clock-setting command. The correction is for this node only. If the node
-        clock later syncs or jumps, delete and queue the schedule again.
+        clock-setting command. The correction is for this node and this open page
+        only: it is never added to generated URLs, and is cleared on reload. If
+        the node clock later syncs or jumps, delete and queue the schedule again.
       </p>
 
       <div class="preset-test-grid preset-test-grid--clock">
diff --git a/test/test_preset_test.js b/test/test_preset_test.js
index 5728adb9..4385e91b 100644
--- a/test/test_preset_test.js
+++ b/test/test_preset_test.js
@@ -35,6 +35,10 @@ const defaults = tool.configFromSearch("", "America/Los_Angeles");
 assert.strictEqual(tool.hasPresetParameters(""), false);
 assert.strictEqual(tool.hasPresetParameters("?"), false);
 assert.strictEqual(tool.hasPresetParameters("?utm_source=example"), false);
+assert.strictEqual(
+  tool.hasPresetParameters("?node_clock=1790044920&node_clock_at=1790034120"),
+  false
+);
 assert.strictEqual(tool.hasPresetParameters("?freq=911.3"), true);
 assert.strictEqual(tool.hasPresetParameters("?tz=UTC"), true);
 assert.strictEqual(tool.hasPresetParameters("?start=bad"), true);
@@ -128,6 +132,12 @@ assert.strictEqual(
   adjustedCommands.stockNow,
   tool.commandsFor(clockAdjustedLink, clockAdjustedLink.startMs).stockNow
 );
+const pageOnlyClockUrl = new URL(tool.configuredUrl(
+  clockAdjustedLink,
+  "https://example.test/preset-test/"
+));
+assert.strictEqual(pageOnlyClockUrl.searchParams.has("node_clock"), false);
+assert.strictEqual(pageOnlyClockUrl.searchParams.has("node_clock_at"), false);
 assert.throws(
   () => tool.schedulerEpochs(clockAdjustedLink, tool.SCHEDULER_EPOCH_MAX),
   /outside the firmware range/