Because this circuit can generate a very loud tone, a 5K potentiometer can be used to turn down the volume. Press the (normally open) test button to validate that the tone circuit works properly ...

Link to Vojtě ch Janásek's article, “Low-distortion oscillator tests measurement circuits.” Today’s 20-bit to 24-bit ADCs need low-distortion signals for testing how well the ADCs digitize analog ...

This Idea For Design shows how a gyrator circuit can be used to perform certain ac tests on units under test that require a dc-current feed.