> Install a low pressure sensor at the wall of an empty barn, provide a
> somehow good windows automatic sealing during measurement, boom a "x"
> liters of 2 to 5 PSI into the barn, measure the delta pressure.  You got
> the first reference.

I feel compelled to point out that the effects on the barn would be similar
to a nearby nuclear bomb.. This may make counting the chickens somewhat
problematic.