The Greddy shows almost perfect 0 when the ignition is clicked on right before the starter kicks in. It might be a hair under 0. Vacuum I'm not sure about. I'll have to write down the vacuum readings and find some kind of conversion chart online or something to see if they are the same. If I'm correct, the Greddy gauge shows mmHg for a vacuum unit of measurement. I'm not too familiar with that one, only PSI, BAR and kg/cm^2, so I've just sort of disregarded what it's been telling me.