The Model 828 AC /D C V-A Source (figure 1) is a compact, seff-regulating voltage and current source, capable of meeting the calibration needs of most measuring instruments and suitable for use in the laboratory, on the production line, or in the field. Three sets of interlocking pushbutton switches permit output mode and range selection. Mode selec­tion provides either dc output or one of three inter­nally generated ac frequencies. If desired, an exter­nal 50-440 Hz signal source may also be used to determine the output frequency. There are four volt­age ranges and five current ranges, and the output can be set to a percentage of the selected range value by a set of thumbwheel switches. The marked value of all ranges can be exceeded by 100%, except the 1000V range which is limited to 1100V maximum, and the 10A range, which is limited to 5 amperes maximum {7 amperes on special order). Two pushbutton switches on the front panel apply and remove the output signal from the output termi­nals. Pressing the OPERATE switch applies the out­put signal to the terminals and lights a green indica­tor lamp; pressing the DE-ENERGIZE switch removes the signal and lights a red indicator lamp. The red lamp will also light whenever the internal protection circuitry automatically removes the output signal from the front panel terminals. A three-position toggle switch allows selection between normal, run up, or percent deviation opera­tion of the Model 828. In the NORMAL position, the output present at the output terminals is exactly the value set by the thumbwheel switches and the range selector, in the RUN UP position, a rotary control permits the operator to vary the output from zero to 102% of the value set by the thumbwheel switches; this allows analog meters to be examined for fric­tional problems in their movements. In the % DEV position, a calibrated control varies the output between 98 and 102% of the value set by the thumb­ wheel switches and provides a direct reading of the percent error of the device under test.