Highly accurate instruments with a calibration are quite expensive, and anything electronic will tend to change over time. The effects of heat and oxidation, and perhaps changes in the material due to current directly. Perhaps there are other reasons circuits change over time.
So I was wondering about some kind of reference that could be built into equipment so it could recalibrate itself. Suppose you wanted to have a fixed power supply that would stay stable at a precise voltage or at least be capable of re-calibration without sending it for expensive recalibration at the factory.
Thinking about what kind of components could be stable, I think a wire-wound resistor with thick connectors and soldered connections. Zener diodes would seem less stable.
So can anyone suggest a way to build a circuit that would provide an extremely stable voltage reference? Given such a voltage reference, I think it would be possible to build an extremely stable power supply.
This question is mostly theoretical out of interest. I'm not asking for a practical design at this point though I wouldn't say no!