What Are Accuracy and Repeatability?

Accuracy means how close a reading is to the real value. Repeatability means the instrument gives nearly the same result when the condition has not changed. A stable wrong reading is still wrong.

A pressure gauge returns to the same mark each day, but a checked reference shows it is several psi off. It repeats well, yet it needs correction or replacement.

The amount of accuracy needed depends on the job. Accuracy is often stated as a percent of full scale: a 0 to 100 psi gauge rated ±1 percent of full scale may be off by up to 1 psi anywhere on its dial, which is a 10 percent error at a 10 psi reading. A rough tank indicator may be fine for a quick field check but not for a compliance total. A laboratory reference may need tighter control than a room thermometer. Operators should know which instruments guide reporting, chemical feed, alarms, or equipment protection. Those devices deserve prompt attention when checks fail. Never adjust a reading only because it differs from what you expected. First confirm the reference and the checking method.

Give compliance and protective instruments the fastest response after a failed check.

Key point: Accuracy is how close a reading is to the real value; repeatability is giving the same result when nothing changed. A stable wrong reading is still wrong.