sorry, as usual i have to disagree.
> So every kind of vacuum measurement (mmHg, torr, mbar or whatever) depends on the
> ambient pressure
this is definitely not true (i object the every): high vacuum measurement works with
conductivity or stuff like that and depends on the type of gas inside the vessel. or how
do you think your barometer works - against which outside pressure would it measure?
chemists aren't interested in the pressure difference at all (as long as the reaction
container survives it). it's all about the force per surface _inside_ the vessel. because
that will matter in respect to where your liquid boils.
> but this is commonly known to be ~760torr or ~1000mbar.
erm, the problem is the "~". suppose i have nice weather and 1010mbar ambient pressure.
i evacuate my vessel to 10mbar and proudly proclaim: "i've got a 1000mbar vacuum!". how
is anyone supposed to know that the weather at my place is nice and i got an ok 10mbar
vacuum instead of an fantastic 0.1mbar vacuum? do you see the problem?
of course cheap vacuummeters are useless for measuring good vacuums.
(and i guess we both agree on the madness of inch Hg or pound per square inch,
relative or not
)