Not sure I understand but see if this is what you want.

Array entered** :

=COUNT(1/FREQUENCY(IF(A1:A10="Model1",B1:B10),B1:B10))

Will count unique serial *numbers* in column B that correspond to "Model1"
in column A.

** array formulas need to be entered using the key combination of
CTRL,SHIFT,ENTER (not just ENTER)

--
Biff
Microsoft Excel MVP


"Brian" wrote in message
...
Howdy All,

I have a workbook that contains service data for units.

Column A = Model Name (alpha) 87 model names that repeat throughout the
column
Column B = Serial Number (numeric), unique number that repeats throughout
the column
Column C = Service Hours
Column D = Service Req Number

Model Name appears many times in column A
Serial Number appears many times in column b.

I want to determine how many of each Model Number I have with a unique
Serial Number.
But each Model Name and Serial Number can occur many times in their
respective columns if there have been multiple Service Requests.


Thanks,
Brian