This circuit uses an LM3909 to produce a precision square-wave signal that is used to calibrate scopes and scope probes or to check the gain and transient response of audio amplifiers (as described in chapter 1). The output is adjustable (with the 1-kΩ pot) and can be held to within a few tenths percent of 1 V.
The output signal is a clean rectangular wave of about 1.5 ms On and 5.5 ms Off.
The 0.01% temperature coefficient of the LM113 regulator results in negligible drift of the waveform amplitude under lab conditions. Because the circuit is battery powered, there is no inconvenient line cord, and no noise or hum. National Semiconductor. Linear Applications Handbook 1991 p 404
Required Field 
