The negative IF is deliberate. Excel will default your variable to false
("not nested"). This means that you don't need to initialise it
specifically.

I dislike negative IFs from a style point of view. But this is one time
when there is a slight technical benefit.

> Looks like only one var is needed for the
> whole Project.

I use one per module, rather than making them global across the whole
project. However it's unusual to need more than one in any single module.

Variable naming is a very personal thing, of course, but I find "NestedCall"
to be pretty descriptive.