they should all be the same.
how are you doing it? cold engine? hot engine?
did you open the throttle body and disable spark and fuel?
You are not "running" any particular Bar, the compression reading is a consequence of the engine internals (i.e what piston/rod/combustion chamber you have) and the health of the engine.
If you have a valve leak you will get a lower figure
If you have slack piston rings you will get a lower figure
both these will produce sliding figures that will gradually drop away when you leave it at TDC. If you want to figure whether it is valve or piston then do a "dry" compression test then a "wet" one by repeating but pouring in a couple of ml of engine oil.
It seals the rings/bore better and you get a higher reading, if it stays the same it's your valves/head.
if you are "3 bar" different between cylinders it is f@cked
they should be within 10% or as close to zero as possible.
If you are running a 10:1 compression engine (Standard N/A) you can expect a 145psi or 10 Bar reading (14.5psi/1 Bar is standard atmospheric pressure, 10x Atmos is 145 or 10)
except your engine runs hot and air heats up when squeezed (put your finger over a bike pump nozzle)
you should see between 170-200psi on a 10:1 c/r engine
none of your engine should be running 10:1 as turbos they will all be between 7 and 9.5 depending on whether they are standard or rebuilt.
the number means nothing unless you have done them the same way.
http://www.pumaracing.co.uk/comp.htm
this is a good write up