Originally Posted by mrphotoman
you have to subtract 14.7 for atmosphere
to really get a good reading you need ot get the barometric pressure form your local airport.... then you need to convert that to psi... here in chicago its closer to 14.5 not 14.7 granted no ones really complaining about .2psi but if some ones boosting 15.8 with your method... they might get a bigger smile knowing its actually 16 lol