Which of the following device is used for indicating the angular speed of a rotating shaft?

- A tachometer is a device for indicating the angular (rotary) speed of a rotating shaft.- A hydrometer or aerometer is an instrument that measures the specific gravity (relative density) of liquids.- A hygrometer instrument is used in meteorological science to measure the humidity or amount of water vapor in the air.- A barometer is a scientific instrument used in meteorology to measure atmospheric pressure.Source: Britannica