A stand-alone instrument that is used to perform a field check of the overall sensitivity of a measurement device. For noise meters, these devices usually produce a single tone at a single frequency but can have multiple frequencies and levels to verify the meter. The most popular level for an acoustic calibrator is 114 dB and an operation frequency of 1 kHz. If a second level is available it is often at a value of 94 dB also at 1 kHz. For air sampling a calibrator can be a rotameter with a floating ball in a tube or a more accurate electronic device that times the flow of a piston in a precisely machined tube.