Ahhh Dan, PSIA has no reference to atmospheric pressure, hence why it's an absolute measurement, it's reference is a full vacuum. Atmospheric pressure at sea level is 14.7 psia.
PSIG is gauge pressure, referenced to atmosphere. Most gauges we'd use on bicycles are referenced against ambient atmospheric pressure.
Feb. 16, 2022, 2:23 p.m. - Tim Coleman
Ahhh Dan, PSIA has no reference to atmospheric pressure, hence why it's an absolute measurement, it's reference is a full vacuum. Atmospheric pressure at sea level is 14.7 psia. PSIG is gauge pressure, referenced to atmosphere. Most gauges we'd use on bicycles are referenced against ambient atmospheric pressure.