boost gauges

[Big_Daddy]

Iver seen some boost gauges on ebay, the mecahnical one from blitz,greddy and apexi.
Some of the gauges are not sitting on zero mark, is this normal? if not are they easy to align or should i just avoid them totaly?

 

[Sidewaysfun]

Out of experience, i've bought a couple of mechanical boost gauges, all of which have not sat on the zero mark. As soon as I've plugged them in though and cranked over the engine, they have sat correctly at the zero level. I think mech gauges do this when not connected to any boost/pressure.

Someone might be able to clarify this?

 

[Big_Daddy]

if not sittin on zero, when you crank engine and idle, it wouldnt be reading the correct vacum pressure?