# eli5: Why do pressure gauges have different units? Why aren’t all gauges standardized to one unit like bar or Pa.

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eli5: Why do pressure gauges have different units? Why aren’t all gauges standardized to one unit like bar or Pa.

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It *should* be standardized to Pascals. Just like all lengths should be standardized in meters. Two reasons it hasn’t happened:

1. Mostly inertia. Different countries and different disciplines have used a unit historically, and see no reason to change.
2. Sometimes units for very large or very small amounts make comparisons easier to grasp. Distance to stars could be expressed in petameters, but light years are simpler to wrap one’s mind around.

Pressure gauges have different units because they are used to measure different types of pressure. Different types of pressure require different units of measure because of the different scales used to measure them. For example, atmospheric pressure is measured in millibars (mbar) while gauge pressure is measured in bars (bar). Additionally, pressure measured in a vacuum is measured in pascals (Pa). Standardizing all gauges to one unit would make it difficult to accurately measure different types of pressure.

Bar and Pa are on the same unit system, 1 Bar is just 100,000 Pa. Provided you’re just using metric you should have the dial measure to bar, millipascals, kilo pascals, mega pascals, etc depending on the magnitude of the thing you’re measuring, so you don’t have a bunch of zeroes on the dial.

Ditto mm, m, km for distance.