query field

[bbcwjun]

I have a field in a Query that makes a calculation (ie. datediff) When I put that field in a form, i would like to be able to change the data in it that shows up but it says Field is based on an expression and cannot be edited...
Is there any way to edit this field or how to put it in a form to edit it? I tried opening the query and editing it also but says same thing??

THANKS