diff --git a/src/mame/drivers/deco32.cpp b/src/mame/drivers/deco32.cpp
index b514831ccbb..54f9c95df2f 100644
--- a/src/mame/drivers/deco32.cpp
+++ b/src/mame/drivers/deco32.cpp
@@ -33,6 +33,10 @@
 
     Tattoo Assassins uses DE Pinball soundboard 520-5077-00 R
 
+    How to calibrate guns in Locked 'n Loaded and Gun Hard:
+    - keep SERVICE1 pressed (default 9) and press the test mode switch (default F2)
+    - complete guns' calibration
+    - exit test mode
 
     TODO: