Frequency meter is an instrument used to measure the frequency of a periodic process. The measured value is displayed on the screen (or other type of display ) in Hz, which is the frequency unit in the SI. Frequency meters can be either analog or digital , as well portable or stationary ones. Analog, vibration and condenser frequency meters belong to the group of electricity measurement appliances. Vibrational frequency meters, for example, are devices from the electromagnetic system, which are operating in the range of 10 up to 1000Hz. Resonant, condenser and electronic frequency meters/counters , on the other hand, belong to the group of radiomeasuring devices.