RPM Indicators are devices used to measure the rotational speed of a shaft or other rotating component. TACHS is an acronym for 'Total Average Counts per Hour System', which is a type of RPM Indicator that uses a sensor to detect the number of revolutions per minute (RPM) of a rotating object. This type of RPM Indicator is commonly used in industrial applications, such as in motors and pumps, to monitor the performance of the equipment.