Originally Posted by tabetha
HG and PSI is merely a different type of measurement, like lbs and kilo's.
Most testing type kit measures in HG, as they traditionally used MERCURY MANOMETRES but this is not the case witha lot of newer kit, when ther gas engineer services your boiler he uses a MERCURY MANOMETRE, but this is down to regulations.
I realise that, but my comment was 'trying' to point out that the gauge is almost certainly going to show the vacuum as a measure of mercury, therefore if they wish to use it for a reference they need to realise that it is a measure of mercury and not Psi............
Since somebody believing the -30 represented psi would not realise it was in fact 1551mm.Hg or mercury...........