But as he says the guage is MARKED in PSI
Be suprised if it does for vacuum..........perhaps he'll confirm
it does not measure "IN" anything it measures pressure, positive and negative
It has an input and an output
Input IS pressure, output is the scale.
They are not evacuated capsule type gauges so therefore MUST have in input.
the markings are then applied after the scale is calibrated to read correctly in WHATEVER SCALE THEY USE, on cars it is PSI/BAR, but just the same as a mercury scale just not as it is choisen by the manufacturer to mark in PSI/BAR.
Well thats a new one on me............ive never seen a Boost gauge with Psi or Bar for a vacuum scale.............perhaps you can post up some pics of them.