diff --git a/README.md b/README.md
index f247484..a3b119e 100644
--- a/README.md
+++ b/README.md
@@ -8,4 +8,6 @@ Since the Goldline protocol uses RS-485, a hardware interface is required. I'm u
 - [Upgrading the AquaLogic Firmware](https://github.com/swilson/aqualogic/wiki/Upgrading-the-AquaLogic-Firmware)
 - [Wired Remote Repair](https://github.com/swilson/aqualogic/wiki/Wired-Remote-Repair)
 
+Tested on an AquaLogic P4 with Main Software Revision 2.91. YMMV.
+
 This project is not affiliated with or endorsed by Hayward Industries Inc. in any way.