I would like to know when formula cells have their calculated values changed
(to update my client program).

Is there an obvious event handler I'm missing?

There's the AppEvents_SheetCalculateEventHandler, but it's signature would
be simply:

private void Calculating(object Sh){...}

(providing only the worksheet the calculate event occurred in).


And although the DocEvents_ChangeEventHandler provides a range,

e.g. private void Changing(Excel.Range target){...}

it does not fire for updates as a result of formula recalculation.



So, presuming that there is no event handler that deals with formula
updates, I can only envisage a solution that requires keeping an internal
collection of all those cells which contain formulae, coupled with their
calculated values and then checking these to see if any changed upon the
AppEvents_SheetCalculateEventHandler event.

Can anyone see a better solution?