Shouldn't be too hard to code something in the BeforeUpdate event for the form control, but that's the limitation (must use a form).
Logic being "if ends with . just remove it, otherwise divide by 100. Not sure, but perhaps you don't have to remove the trailing . Access just might drop it anyway.
EDIT - just tried leaving the . at the end directly in a table - it was just dropped. So even simpler than the posted code?
If Right([fieldnamehere],1) = "." then simply divide?
EDIT 2 - works if it is a whole number only, so not so simple I guess.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.