Desk Top Dyno

I had some SB heads here that had been ported, and the supplied flow numbers showed a 30cfm gain from .500-.600.
I told the owner I didn’t think those heads were capable of the numbers he had gotten.
The heads were coming to me for finishing and assembly anyway, so I tested them.
I checked one cylinder on each head.
From .500-.600, one port gained 7cfm…… the other 5cfm.
And on my bench the better of the two ports was down 38cfm from the numbers he got from the porter.