Actually...

1 Bar = 14.5038 psi ~> http://en.wikipedia.org/wiki/Bar_(unit)

1 ATM = 14.695 948 775 5134

I was just rounding anyway. BAR and ATM are both based on variations of sea level atmospheric air pressure. The oil gauge reads BAR. Its a lot easier to multiply 14.5 in your head, than 14.7.

The French came up with ATM, and while technically more accurate to air pressure, BAR is just simpler. Probably why its taken precedence. Personally however, I would prefer the gauge read PSI.