Final answer:
A high pressure gauge reading 0 to 500 is rated for 500 psig, which indicates the pressure inside a system relative to atmospheric pressure. A reading of zero means atmospheric pressure, whereas any positive reading indicates additional pressure. Gauge pressure differs from absolute pressure, which includes atmospheric pressure in its calculation.
Step-by-step explanation:
If a high pressure gauge's scale reads from 0 to 500, it typically means that the gauge is rated to measure pressures up to 500 psig, where 'psig' represents 'pounds per square inch gauge.' This type of measurement is called gauge pressure, which is the measurement of pressure relative to atmospheric pressure. Most pressure gauges are calibrated to read zero at atmospheric pressure, so positive readings indicate pressure that is higher than atmospheric pressure while a reading of zero signifies atmospheric pressure.
For example, if the gauge reads 0, it means there is no additional pressure in the system above the current atmospheric pressure. On the other hand, a reading of 500 would mean that the system's pressure is 500 psi above atmospheric pressure. Using a tire gauge as an analogy, when your tire is completely flat or has a gaping hole, the gauge reads zero because the pressure inside the tire is equal to the atmospheric pressure outside.
It is important to note that gauge pressure is different from absolute pressure; the latter includes atmospheric pressure in its measurement. When working with pressure systems, e.g., a scuba tank, these distinctions are crucial. A full scuba tank might read 3000 psi, revealing the pressure inside is significantly higher than the atmospheric pressure outside.