The Keithley 2500 Dual Photo Diode Meter combines two stable DC bias voltage sources with two low-noise ammeters for dual-channel, low-current photodiode measurements. The unit has 0.1% basic measurement accuracy with up to 6½-digit resolution. At 5½-digit resolution, the Model 2500 can transfer up to 475 readings per second over the GPIB, and up to 900 readings per second with 4½-digit resolution.