finally got it - now what?

[speedyd1]

i finally finished my bench. it is patterned after the one in car craft. similar not exact. my question is -
can i use a known orifice to calibrate my bench and how.
lets say for example i have a 2" orifice that flows ??? at ??? in.
i place it on top of the bench, i pull the vacuum up untill i get ??? in. i then set my inclined manometer using a metric tape so that the level is exactly at 100. it reads 1 - 200.
if i then measure a head or something at the same pressure drop and it now reads 120. can i assume that it is flowing 120% of the calibrated flow figure known from the orifice.
is that even logical?