>I am using buffering, but in this app it is possible that the user will change the value in the field several times. As I understand it, OLDVAL() returns the value that you got when you started the screen. This means recalculation would fire every time the current value in the textbox was compared to oldval() (assuming the user had made a change). When exactly does the control update the underlying field or variable???

When you issue Tableupdate() for field, and when control loses focus for variable.