diff --git a/firmware/controllers/algo/event_registry.h b/firmware/controllers/algo/event_registry.h
index af1c963d91..0ff7fd71f7 100644
--- a/firmware/controllers/algo/event_registry.h
+++ b/firmware/controllers/algo/event_registry.h
@@ -50,6 +50,9 @@ public:
 	 * @see globalSparkIdCoutner
 	 */
 	int sparkId;
+	/**
+	 * [0, specs.cylindersCount)
+	 */
 	int cylinderIndex;
 	char *name;
 #if EFI_UNIT_TEST || defined(__DOXYGEN__)