A method of determining characteristics of transistors and electroluminescent devices, includes: providing an electroluminescent display; providing for pairs of electroluminescent devices drive circuits and a single readout line, each drive circuit including a readout transistor electrically connected to the readout line; providing a first voltage source; providing a second voltage source; providing a current source; providing a current sink; providing a test voltage source; providing a voltage measurement circuit; sequentially testing the drive transistors to provide a first signal representative of characteristics of the drive transistor of the first drive circuit and a second signal representative of characteristics of the drive transistor of the second drive circuit, whereby the characteristics of each drive transistor are determined; and simultaneously testing the first and second electroluminescent devices to provide a third signal representative of characteristics of the pair of electroluminescent devices, whereby the characteristics of both electroluminescent devices are determined.