I need to get a UDF to sometimes return its existing value rather than
recalc. I am happy for the function to be called but need some way of 1)
bypassing the full calc - (clearly trivial) and then 2) returning the value
that was already there before the calculation attempt (much harder!)

This is really for speed increases. I have a set of Excel functions that
query an Access based app and users typically have many huindreds of calls in
a single wrokbook. The underlying data in the mdb only changes occasionally
(but unpredictably)