diff --git a/ur_msgs/msg/Analog.msg b/ur_msgs/msg/Analog.msg
index 9015f6c49eadcaec438c39ca1c3343073963a80d..2a33752218ff9e5c29c37d25672255077de6cccb 100644
--- a/ur_msgs/msg/Analog.msg
+++ b/ur_msgs/msg/Analog.msg
@@ -1,2 +1,6 @@
+uint8 VOLTAGE=0
+uint8 CURRENT=1
+
 uint8 pin
+uint8 domain # can be VOLTAGE or CURRENT
 float32 state