diff --git a/tally.1 b/tally.1
index 4e71f9e..e818b18 100644
--- a/tally.1
+++ b/tally.1
@@ -93,6 +93,10 @@ u
 Underline the value of the currently selected cell.
 .TP
 .B
+O
+If the selected cell contains a URL, will attempt to open the URL in the system's default browser (will only work in a graphical environment). If the cell does not contain a URL there is no effect.
+.TP
+.B
 :
 Enter command mode (will prompt for command).
 .SS  LINE COMMANDS