Thread: Simple count of number of different values

I've searched, and so many counts are conditional, requiring other columns for look-ups, or "hard-coded" criteria ("w") embedded in the formula.

I want a simple count of a single column. But I want to know how many different things are in that column - not a list. So if I had
A
A
B
A
D
C
A
I would get "4" -
Nothing I've tried has worked - formula-wise. I can do this with sub-totals, collapse [2], "visible cells only" copy/paste to another sheet to see how many rows are consumed...but that's much to cumbersome to perform regularly.
sample file attached.
thanks for any assistance!