diff --git a/automotive/vehicle/2.0/types.hal b/automotive/vehicle/2.0/types.hal
index 931fee4..da48b3c 100644
--- a/automotive/vehicle/2.0/types.hal
+++ b/automotive/vehicle/2.0/types.hal
@@ -3691,7 +3691,10 @@
  * events.
  */
 struct VehiclePropValue {
-    /** Time is elapsed nanoseconds since boot */
+    /**
+     * Time is elapsed nanoseconds since boot. It's equivalent to
+     * {@code SystemClock.elapsedRealtimeNano()}.
+     */
     int64_t timestamp;
 
     /**