I have a list of Purchase Orders Codes (alpha-numeric data) and I want to
know how many different POs are being hit in a list of monthly purchases. For
example:

EV134
SD234
EV134
WD686
WD686
EV134
SD234
HK128

So, the answer I would be looking for is 4. Is there a easy way to do this?
I have a formula that calculates this with numbers, but the text seems to
mess it up.

Any help would be appreciated - Thanks - P