Now I understand the question. Gauge pressure, used by common pressure gauges is referenced from the atmospheric pressure of the day being zero PSI. Atmospheric pressure or absolute pressure scales are used in barometers and referenced to an absolute vacuum, zero PSIA. In general pressure measurment the variance in atmospheric pressure is negligible but this small pressure change does have effect in altitude, temperature, and density of the air. The difference is 4.5 PSI from sea level to 10000 feet. This is why quality pressure gauges in PSI have a zero adjust.