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.
If you have a typical vacuum furnace it is normal to have at least three electronic vacuum gauge heads mounted on the system to monitor the level of vacuum at selected positions. These gauge heads send signals back to the controls system 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. To many casual observers the readings and names of the measuring units being used are like a foreign language, and they may well be because many names were derived in Europe. Let’s take a look at the different vacuum measurement units in use around the world and where the names came from.