You could set up a script trigger to format it when the field is saved.
Thanks Eric. Is there a way to have it display "on the fly?"
"on the fly" as in keystroke by keystroke? That would be difficult as there's no way for the code to know where to put the decimal point unless every value is always the same number of digits. (enter 0900 for 9.00 for example )
An auto-enter calculation could add the missing decimal if none were input, though users would need to consistently type in the same number of digits after the decimal for every number input. (Is 335, 33.50 or 3.35? )
If ( PatternCount ( Self ; "." ) ; Self ; Left ( self ; Length ( self ) - 2 ) & "." & Right ( Self ; 2 ) )
(Clear the do not replace existing values check box if you want this to apply even after editing an existing value in the field.)
Thanks Phil. So far, it's working well.