The Keithley SMU was purchased in 1996 with funds from the NSF-ILI program. An SMU is basically a sophisticated digital multimeter and power supply in one unit, combined with a computer for logging data. The unit may be set up to perform a series of voltage measurements while it sweeps current or a series of current measurements while it sweeps voltages. Measurements may be performed over a wide range of sweep rates. The unit is controlled by a computer using the gpib and is intended to be used with the monochromator for performing quantum efficiency and J-V measurements on solar cells.