well, you certainly could use a manometer to check the crankcase pressure, and that would be useful too. All you need is a piece of clear plastic tubing, attach to pressure source, loop it into a "U" shape and pour a few inches of water in. The difference in water levels from 1 side to the other is the pressure differential. About 27.7" water=1 psi. However, I think that a better indicator of cylinder blowby can be had by measuring FLOW rather than PRESSURE. My engine for example, generates relatively low blowby FLOW, (I believe), yet can generate relatively high PRESSURE, as the valve cover, crank seals, oil pan seals, etc. are really tight, perhaps as evidenced in the last picture I posted here which shows the bag connected to the crankcase still pressurized 20 minutes after engine shutdown. An older, leaky engine with a lot of blowby will generate much higher FLOW and pressure be a function of both cylinder blowby and seal condition.

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.