You can use the Red Lion Cub 5 Series digital rate meter. This will provide you with a digital readout of the speed at the motor/gearmotor driveshaft, from the tachometer output on the control. The rate meter is battery powered, and can be programmed to know how many pulses it will receive per unit output and to display speed in RPM. Our tachometer output provides the meter with 12 pulses/motor revolution. To calculate the resolution of the tachometer output with respect to the driveshaft of a gearmotor, multiply the gear ratio by 12.