diff --git a/firmware/controllers/trigger/rpm_calculator.h b/firmware/controllers/trigger/rpm_calculator.h
index fd8078c08a..efdab6cb31 100644
--- a/firmware/controllers/trigger/rpm_calculator.h
+++ b/firmware/controllers/trigger/rpm_calculator.h
@@ -88,6 +88,7 @@ public:
 	int previousRpmValue;
 	/**
 	 * This is a performance optimization: let's pre-calulate this each time RPM changes
+	 * NaN while engine is not spinning
 	 */
 	volatile floatus_t oneDegreeUs;
 	volatile efitime_t lastRpmEventTimeNt;