# What are the different reference modes in pressure calibration? **URL:** \ **Category:** Calibration\ **Tags:** calibration, pressure\ **Created:** [January 11, 2017, 4:07am UTC](https://forumautomation.com/t/what-are-the-different-reference-modes-in-pressure-calibration/1646 "2017-01-11T04:07:30Z")\ **Posts on this page:** 1\ **Page:** 1
**Author:** ![denizen](https://forumautomation.com/letter_avatar_proxy/v4/letter/d/848f3c/32.png) [@denizen](https://forumautomation.com/u/denizen)\ **Post date:** [January 11, 2017, 4:07am UTC](https://forumautomation.com/t/what-are-the-different-reference-modes-in-pressure-calibration/1646/1 "2017-01-11T04:07:30Z")
The reference modes are Gauge,Absolute and Differential. **Gauge Mode** Referenced to atmospheric pressure. 0 means your test pressure is the same as atmosphere. Gauge mode is the most common reference mode. Can be both positive and negative.Usually the easiest to measure. ![](https://cdn.forumautomation.com/original/1X/0ea4de0aa459c262aa74d07d9aaff3768fbec35e.jpg) **Absolute Mode** Referenced to a perfect vacuum. 0 means that it is a perfect vacuum.Absolutely no molecules. Can only be positive numbers. You cant have negative molecules in a vessel. More difficult measurement. ![](https://cdn.forumautomation.com/original/1X/4cc30f39449825a1e9fe8c765086279a1b887133.jpg) **Differential Mode** Referenced to another pressure. Eg: line pressure. 0 means that there is no difference in the two pressure. Gauge mode can be thought of as a special case of differential mode. Can be a difficult measurement to make. Can be both positive or negative. ![](https://cdn.forumautomation.com/original/1X/1150c31081351dfc43a25d645193c90d1e31de2c.jpg)