diff --git a/Documentation/ABI/testing/sysfs-bus-iio b/Documentation/ABI/testing/sysfs-bus-iio
index df5e69e6247c44f06330c3f0040b7c73724c5d18..831db8623e4b71dc6dc777022ad25364716e3020 100644
--- a/Documentation/ABI/testing/sysfs-bus-iio
+++ b/Documentation/ABI/testing/sysfs-bus-iio
@@ -1068,7 +1068,9 @@ Description:
 		reflectivity of infrared or ultrasound emitted.
 		Often these sensors are unit less and as such conversion
 		to SI units is not possible.  Where it is, the units should
-		be meters.
+		be meters.  If such a conversion is not possible, the reported
+		values should behave in the same way as a distance, i.e. lower
+		values indicate something is closer to the sensor.
 
 What:		/sys/.../iio:deviceX/in_illuminanceY_input
 What:		/sys/.../iio:deviceX/in_illuminanceY_raw