diff --git a/app/src/main/java/com/onthelevel/OnTheLevelApp.kt b/app/src/main/java/com/onthelevel/OnTheLevelApp.kt
index 038ea21..50aad57 100644
--- a/app/src/main/java/com/onthelevel/OnTheLevelApp.kt
+++ b/app/src/main/java/com/onthelevel/OnTheLevelApp.kt
@@ -22,8 +22,13 @@ class AppContainer(context: Context) {
      * Outlives any single screen. Used for durable fire-and-forget persistence
      * (e.g. saving a calibration): a screen-scoped coroutine would be cancelled if
      * the user leaves the moment the write is launched.
+     *
+     * Main.immediate (not Default) so writes launched from UI callbacks enqueue in
+     * call order — two fast conflicting writes (recalibrate then Reset) then reach
+     * DataStore deterministically. Only lightweight persistence runs here; DataStore
+     * still performs the actual IO on its own dispatcher.
      */
-    val applicationScope = CoroutineScope(SupervisorJob() + Dispatchers.Default)
+    val applicationScope = CoroutineScope(SupervisorJob() + Dispatchers.Main.immediate)
 
     val sensorSource: SensorSource by lazy { AndroidSensorSource(appContext) }
     val settings: SettingsRepository by lazy { SettingsRepository(appContext) }