Calibrating pressure instrumentation is one of the commonest forms of calibration that laboratories and industrial facilities perform. The calibration equipment for moderately accurate calibrations is relatively inexpensive, rugged, and easy to use. The wide range of pressures that may be measured in one facility will require more than one type or range of calibration standard. The pressure range from one inch of water to 100,000 pounds per square inch, for example, represents a 2.77 million-to-one ratio of maximum pressure to minimum pressure. The number of standards needed is also increased if vacuum and absolute pressure calibrations are required and if various fluids such as water, oil, and gas are required.

Pressure is a derived unit based on the fundamental units of length (l), mass (m), and time (t). Earlier chapters of this book defined pressure as a force acting on an area (l ²), defined force as a mass (m) being accelerated, and defined acceleration as (l/t ²). The accuracy of many of the pressure standards depends on how accurately we can produce, maintain, and measure these fundamental units when manufacturing and using the standards.