In reply to:

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Anyway preasure;
1000ft = 304.8m
preasure at 304.8m = 30.48 bar + 1bar for atmospheric preasure.
so preasure would be 31.48 bar or 456.47 Psi (if you like it in old numbers)

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But pressure differential would still be 30.48 bar in medium old numbers, or around 3MPa (megapascals) in new numbers (our weathermen report air pressure in hPa - hectopascals - secret aliases for millibars).
(1 bar ~ 1 kg * 9.8 m/s**2 / cm**2 = 9.8 N/cm**2; 1 Pa = 1 N/m**2 ~ 10/1000**2 = 1e-5 bar)

As everibody has guessed by now, I am procrastinating. I have a report to write for tomorrow. Ah, well...

Cheers!

Dragi "Bonzi" Raos
Zagreb, Croatia
Q#5196, MkII#80000376, 18GB green