I have a function in a cell triggered on the value returned by a DDE
link in another cell.

e.g. cell A1 contains =function1(A2) and cell A2 contains
=ADVFN|NYSE_CAT!CUR

function1 is triggered each time the DDE link updates regardless of
whether the result returned has changed or not. How do I prevent
function1 being triggered if the returned value has not changed?

Thanks