Count Unique Fields in Access Report

[alynn1976]

I am working in an Access report. I need my text box control source to calculate the number of tractor names without duplicates. For example:
Tractor1
Tractor2
Tractor4
Tractor1
Tractor1
I would need the total to be 3 instead of 5.

I can find a formula for this.

[June7]

Build a query object: SELECT DISTINCT fieldname FROM tablename WHERE some criteria here;

Expression in textbox: =DCount("*", "queryname")