Is there any event that would detect a user hiding or unhiding columns?

I have a graph that plots data together with some computed quantities.
I want the computed quantities to reflect only the data that is visible
on the graph (from columns that are not hidden). I wrote an IsVisible()
function to make the computations use only the visible data, but
hiding/unhiding columns does not trigger a recalculation, even if
IsVisible() is declared Volatile.

Jerry