DUTs; in this way, two DUTs can be "matched" for optimum performance in circuits (such as differential amplifiers) which depend upon the close matching of device parameters. This can be seen in the adjacent image where a toggle switch allows the rapid switching between the DUT on the left and the DUT on the right as the operator compared the respective curve families of the two devices. I-V curves are used to characterize devices and materials through DC source-measure testing. These applications may also require calculation of resistance and the derivation of other parameters based on I-V measurements. For example, I-V data can be used to study anomalies, locate maximum or minimum curve slopes, and perform reliability analyses. A typical application is finding a semiconductor diode's reverse bias leakage current and doing forward and reverse bias voltage sweeps and current measurements to generate its I-V curve. Kelvin sensing Curve tracers, especially high-current models, are usually supplied with various semiconductor device test fixture adapters that have Kelvin sensing. Capacitive balance control Some analog curve tracers, especially sensitive low-current models, are equipped with a manual control for balancing a capacitive Bridge circuit for compensating ("nulling") the stray capacitances of the test setup. This adjustment is performed by tracing the curve of the empty test setup (with all required cables, probes, adapters and other auxiliary devices connected, but without the DUT) and adjusting the balance control until the I curve is displayed at a constant zero level. I-V Curve Tracing I-V curve tracing is a method of analyzing the performance of a Photovoltaic system, ideal for testing all the possible operating points of a PV module or string of modules. History Before the introduction of semiconductors, there were vacuum tube curve tracers (e.g., Tektronix 570). Early semiconductor curve tracers themselves used vacuum tube circuits, as semiconductor devices then available could not do everything required in a curve tracer. The Tektronix model 575 curve tracer shown in the gallery was a typical early instrument. Nowadays, curve tracers are entirely solid state and are substantially automated to ease the workload of the operator, automatically capture data, and assure the safety of the curve tracer and the DUT. Recent developments in semiconductor curve tracer systems now allow three core types of curve tracing: current-voltage (I-V), capacitance-voltage (C-V), and ultra-fast transient or pulsed current-voltage (I-V). Modern curve tracer instrument designs tend to be modular, allowing system specifiers