Piezoelectric resonators are sold as separate components for use in crystal oscillator circuits. It measures temperature by measuring the frequency of a quartz crystal oscillator. A crystal oscillator is used in coding. Cady built the first quartz crystal oscillator in 1921. The basic element for time generation is a quartz crystal oscillator. It, too, required an external crystal oscillator. This test method applies to implantable medical devices, crystal oscillator, saw filter devices. Typically a TDC uses a crystal oscillator reference frequency for good long term stability. One of the most common piezoelectric uses of quartz today is as a crystal oscillator. The first quartz crystal oscillator was built by Walter G. Cady in 1921. An NTSC or PAL television's color decoder contains a colorburst crystal oscillator. Meacham's circuit included a quartz crystal oscillator and a lamp in a Wheatstone bridge.