Validate - Test for any invalid entries. This does not check for incorrect entries. Invalid cells are hilighted in pink.
Check All - This is a cheat button. It performs the 'Validate' above and then tests for incorrect entries. Any cell with the wrong number is hilighted in red.
Restart - Resets the puzzle back to the original starting point.
Mark - This allows you to bookmark the current puzzle state. You can have as many bookmarks as needed.
Back - Restores the puzzle back to the latest bookmark.
Restore - Restores the puzzle back to the latest bookmark and removes that bookmark from the stack.
Purge - Clears all of the bookmarked save points.
Help - Displays/Hides this help.
Easy, Medium, Hard, Extreme - Selects new puzzle and level.