What is the difference between 700G and 700GA Pressure Gauge Calibrators?
Why can’t I zero out the 700GA pressure gauge like I can with the 700G models?
The 700G’s are a ‘gauge’ pressure gauge, and they will only measure what the gauge itself is being subjected to directly.
The 700GA's are an 'absolute' pressure gauge, and they will always report gauge pressure AND the atmospheric pressure of the world around it.
When you press [ZERO] on a regular 700G, it sets the gauge pressure to zero. Any further pressure applied or removed will be relative to this new zero.
When you press [ZERO] on a 700GA, however, it instead is used to set the barometric reference pressure.
The only way for one of the absolute gauges to show zero is to be hooked up to a vacuum pump and have them experience a vacuum.
Average atmospheric pressure at sea level is 14.7 PSI, so a 700GA might often show a measurement like this.