Despite what people may think about crystals and their stability issue, as with all things, high tolerance, good stability and frequency stable crystals can be purchased at a price. Most crystals that were designed for standard microprocessor based applications were never intended for high stability / accuracy apps. These crystals tend to have a frequency stability range between 250ppm - 50ppm / C.
I purchased a 10Mhz crystal not so long ago that has a stability factor of 1ppm/C. At 10Mhz, it drifts 10Hz per C, which for accurate timing applications would be more than enough.
Search through electronic suppliers catalogues for crystal specs and you should see what I mean.
Paul.
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