Hg is the chemical shorthand for mercury, and at sea level, atmospheric pressure is sufficient to hold up a column of mercury of about 760mm. (mm being metric short hand for millimeters.) In english measurements this amounts to something like 29.9 inches of mercury. A full vacuum would go down to 0mm or 0" of mercury, however you can only approach that out in space or with very high $$$ specialty vacuum pumps. Atmospheric pressure is about 14.7psi at sea level, and a post earlier in the year discussed what a bar is.

__________________
1961 190Db retired
1968 220D/8 325,000
1983 300D 164,150

dang, someone already read and answered my stupid question before i could delete it!

ok, im an idiot, my mityvac only reads psi on the pressure side, and "hg on the vac side. and it doesnt read atm either, its kpa.

thanks alot for your patient and insightful answer though. and i do know what mm stands for, but thanks.

__________________
1991 300 D 2.5 Turbo, 220k
also in the family:
1981 240 D 185k
1991 350 SD 185k
2006 S 500
2005 SLK 350

Thanks for the responses. Rest assured the '87 has been off the road for weeks.

Grdenko,
Was only funnin on the mm. As a Chem. E in a previous life, one of my gripes is the need to deal with so darn many units of measure for the same physical property. Metric didn't help and is really no better than the "British " method except in the money arena and they have left shillings behind anyway. In fact the fahrenheit temp scale is nearly twice as good as Centipede when it comes to resolution. Oh well......

__________________
1961 190Db retired
1968 220D/8 325,000
1983 300D 164,150

right on

__________________
1991 300 D 2.5 Turbo, 220k
also in the family:
1981 240 D 185k
1991 350 SD 185k
2006 S 500
2005 SLK 350

Rest assured, the 87 has been off the streets for weeks. Thanks for your inputs; ordered the master cylinder last night.