Source: Vacaero.com
"Vacuum gauges all measure the pressure readings in the range from atmospheric pressure down to some lower pressure approaching absolute zero pressure, which is not attainable. Some gauges read the complete range and others can only read a portion of the range, usually used for very low pressures."
A typical vacuum furnace can have at least three electronic vacuum gauge heads to monitor the level of vacuum at various positions. These gauges send signals back to the control systems, and "the vacuum readings are used to ensure that the vacuum pumps are working correctly and that the process chamber is at the correct low pressure (vacuum) for the specific process."
In this Heat Treat Today Best of the Web feature, VAC AERO International shares how different vacuum measurement units are being used around the world today.
Read more: Understanding Vacuum Measurement Units