Guitar pickup test instrument
The V5.8 integrator circuit provides a high impedance preamplifier, an integrator, and an output amplifier. It also has switches to control input gain, and to select between internally provided test loads. One of the loads is a large capacitor, to measure inductance, and the other is an RC load to simulate a typical guitar circuit. A three way switch can select between these two loads, or neither load in order to make an unloaded (actually minimally loaded) measurement.
For more details, read the wiki: https://github.com/KenWillmott/integrator/wiki