[sdiy] expo accuracy? or integrator accuracy?, or both?

[Grant Richter]

> What is the objection to mica? I have never understood that. Cornell
> Dubilier specs some units at 25 ppm/K drift.  The good "pure India ruby
> muscovite mica" units cost several dollars.  Other grades may be inferior.
> 
> In addition to the absorption (dissipation) effect you note, there can also
> actually be hysteresis or memory effects.
> 

You might also want to look at Glass-Ceramic COG types 0 ppm +/- 30 ppm.
Corning used to make them for the Space program.

Not sure the difference between COG and NPO, have tried both in place of
polystyrene with equivalent tracking performance.