The Ando AQ2141 optical multimeter expands the Ando AQ2140 to support external units. It can hold up to four channels for the Ando AQ2140 optical multimeter, including sensor units, OPM, or light source units. A maximum of four expansion frames can be connected to the Ando AQ2140 control unit. The AQ2141 can also be used as a multi-channel light sources by itself. (It does not support ATT function or 1 kHz or 2 kHz chopped light).