The SPDRO-4 is a digital tachometer that can be used with any of Anaheim Automations brushless drivers/controllers. It has a power input that ranges from 12-48VDC so it can use the same power supply as the driver/controller. There is one input on the SPDRO-4 that connects to Hall A, Hall B, Hall C, or PG out. This input is rated from 3.5VDC to 24VDC. This tachometer has a 4 digit display so it can show the speed from 0 to 9999 RPM. The SPDRO-4 allows you to verify the speed of any brushless motor without connecting to a computer or using an external tachometer on the motor itself. The SPDRO-4 has a mode button which allows you to change the value of the motor poles between 1, 2, 4, 6 and 8 and the gears from 1-999. A gear ratio of 1 is for no gear box.