COUNTIFS - But only count once for each like item

Current formula:
=COUNTIFS($H:$H,"Procedure",$B:$B,">="&$M$3,$B:$B,"<="&$N$3)

Where:
H:H = General format
B:B = Date format
M3 = Low Date
N3 = High Date

Basically, I am currently using this to report how many instances of the word "Procedure" occurs in column H for a date range (M3 - N3).

However, I would like to remove the H:H, "Procedure" criteria and instead count by procedure form number stored in column F (general format).

Any given procedure form number (ex: RSPW-8HZP7F) could be listed multiple times. I would like to increase the count by 1 only if the form number has not been counted before. So although a specific form number may be listed 5 times, I only want to count it once.

Any thoughts on how to achieve this?

Thanks!!
Ryan