Phase meters (phase testers, phase rotation meters) check the phase sequence and phase orientation in three-phase electrical systems. They are used for energy measurements, and the monitor the quality of audio and video transmissions. Correct phase matching is also important in energy metering applications since phase mismatches between channels may cause significant measurement errors at low power factors. Bandwidth, sampling rate, maximum channels, and operating temperature are important parameters to specify when selecting phase meters. Bandwidth is the frequency range over which current or voltage is measured. Sampling rate is the frequency that a digital meter tests an analog signal and converts to a digital value.