If you use a script trigger, such a result might be set up. It's easier in FileMaker 11, where you can use the OnObjectSave trigger--only fires when the value is actually changed, but if you capture the current value in a variable when you enter the field and compare it to the value when the field is exited, your script can determine whether or not to update with a new date.
Thanks for the reply. I am going to update to FM 11 soon. This may push me to it.
Is there are place where I can get this script for FM 10?
Use OnObjectEnter to save the current value in a global field.
Set Variable [$$originalValue ; Value: YourTable::YourField]
Test this carefully, we found a bug with script triggers and certain field formats (drop down list or pop up menu--I forget which) where we had to pass the field's current value as a parameter to the script. We put YourTable::YourField as the parameter and then used:
Set Variable $$Originalvalue ; Value: Get ( ScriptParameter ) ]
To capture the original value.
Once you have the original value saved in a global variable, OnObjectExit can do this:
If [$$OriginalValue ≠ YourTable::YourField ]
Set Field [YourTable::YourModDateField ; Get ( CurrentDate ) ]
With FileMaker 11, I think you can get away with just the second script assigned to the OnObjectSave trigger.