Magtrol Models 5500 and 5501 are manually-operated switch boxes that permit the connection of up to three Magtrol Dynamometers to a single DSP7000 Dynamometer Controller. Use of the switch boxes facilitates quick and easy interfacing of multiple dynamometers without the necessity of disconnecting and reconnecting the brake and control cables. For Magtrol WB Eddy-current or PB Powder Brake Dynamometers, BOTH a 5500 AND a 5501 Switch Box are necessary. Magtrol HD or ED Hysteresis Dynamometers only require the 5500.