The Debug Button changes the screen from "Normal" mode to "Debug" mode.
In "Debug" mode, all the linkage fields are shown, screen lock is turned off
(allowing you to see lots of annoying card flipping), and the menubar is shown. In "Debug" mode, the field called "Data" is hidden.
In "Normal" mode, all the linkage fields are hidden, screen lock is turned on, and the menubar is hidden (in order to keep users from being tempted to use the card add/delete funtions found on the Edit menu).