diff --git a/marine_sensor_msgs/msg/RadarEcho.msg b/marine_sensor_msgs/msg/RadarEcho.msg
index ae2a80a..629c11b 100644
--- a/marine_sensor_msgs/msg/RadarEcho.msg
+++ b/marine_sensor_msgs/msg/RadarEcho.msg
@@ -3,5 +3,9 @@
 # single ray.
 
 # Series of intensities from closest to farthest
-# along a given angle increment. [device-specific units]
+# along a given angle increment. For interoperability,
+# values should be normalized from 0.0 to 1.0.
+# Exceptions to using normalized values should be well
+# documented in the device driver and supporting software.
+# [device-specific units]
 float32[] echoes