Globally there are a great many derived units of measurement for pressure in wide use, although pressure is often expressed as a force per unit area. The unit of pressure most familiar to divers in the US is pounds per square inch (psi), while bar is widely used by divers in the European Union. Many divers accustomed to the metric system are surprised to learn that bar is an archaic unit of measurement for pressure that is deprecated, replaced by the Pascal.
There is no convenient order-of-magnitude equivalent to bar in Pascal (Pa), the closest being one bar is exactly 100 kiloPascal (kPa). Expressed as force per unit area, one bar is ≈1.02 kilograms per square centimeter (kg/cm2) in the metric system, which is pretty close. Many divers think about pressure in terms of height of a column of sea water: one bar is defined as exactly 10 meters of sea water (msw) or ≈32.6 feet of sea water (fsw). Some partial pressure diving calculations are more convenient when performed using a unit of pressure known as atmospheres (atm): one atm is ≈1.01 bar or ≈14.7 psi. Given the relative accuracy of the diving devices we are using for measurement these are close enough that we've seen many divers interchangeably use 1 bar, 1 atm, 1 kg/cm2, 15 psi, 10 msw and 33 fsw as all equivalent, although this may distress the scientists and engineers among us.