>I need to know what the previous value was in a field for processing and comparison routines. I assume I can use the TAG property to store the value before entry (using the GOTFOCUS method) and check it in before exiting (LOSTFOCUS). Is that the recommended way?

Usually the WHEN and VALID methods are used, respectively, for this purpose. Using the VALID method has the advantage of being able to return .F. if the validation tests aren't passed, so that the control can't lose the focus until the data passes validation.

>I also noticed that the TAG property is usually text... if I am storing a value, such as a dollar amount, do I need to use the STR & VAL routines to convert it or is there a way to get the TAG to be something other than text?

Yep, the TAG property is always text. You could use conversion functions as you said, but I find it's easier to simply add a property to the form or formset -- usually I just call it "PrevVal" and use it wherever I need to temporarily store a previous numeric value for comparison.