Oven-stabilized crystal oscillators are a time-honored technique for precision electronics. It turns out that no matter how carefully you stabilize a circuit f

Oven-stabilized crystal oscillators are a time-honored technique for precision electronics. It turns out that no matter how carefully you stabilize a circuit for temperature changes, it gets much more stable when held at a controlled temperature. Arrangements for this go from simple (gluing the component to a PTC thermistor driven at constant voltage) to elaborate (thermocouple-controlled PID heater in multiple styrofoam insulating enclosures). There are some pictures at https://en.wikipedia.org/wiki/Crystal_oven https://en.wikipedia.org/wiki/Crystal_oven I've never seen PCB traces used for this, but I've always wanted to try making a clock from a piece of LCD color-change material laminated to a PCB with traces in seven-segment patterns.