Calibration plate

[bigblock57]

Not sure if this has been covered before but when I check my calibration plate on the bench with no adapter compared to on top of my 4" bore adapter I read about 15 cfm higher on the bore adapter to mounted on top of the bench.
Can any one tell me which is the best method to use
on top or the bench or on top of the adapter you are going to use to flow the head
Thanks

[Brucepts]

Sitting right on top of your flowbench no adapter.

The adapter will change the Cd of the calibration plate based on it's diameter in relation to the orifice diameter (beta ratio)

[bigblock57]

Thanks Bruce