diff --git a/Event/xAOD/xAODForward/xAODForward/versions/AFPToFHit_v1.h b/Event/xAOD/xAODForward/xAODForward/versions/AFPToFHit_v1.h
index ba6dd59fca7729c91533c862a6e61fab37edbc1d..bbbbc3f7b01db0df38b6396ea8075b0315ef8241 100644
--- a/Event/xAOD/xAODForward/xAODForward/versions/AFPToFHit_v1.h
+++ b/Event/xAOD/xAODForward/xAODForward/versions/AFPToFHit_v1.h
@@ -64,8 +64,10 @@ namespace xAOD {
     /// @brief Lenght of the signal pulse which is proportional to the signal
     /// amplitude
     ///
-    /// The returned value is roughly lenght of the signal above
-    /// threshold expressed in nanoseconds.
+    /// The returned value is lenght of the signal above
+    /// threshold expressed in nanoseconds. Available values should be
+    /// multiples of 0.521. Pulse lenght of 1 nanosecond corresponds
+    /// roughtly to signal of about 67 mV.
     float pulseLength() const;
 
     void setPulseLength(float pulseLength);