>Actually high frequency oscillators are very sensitive to environmental variations, especially temperature, that will cause them to "drift" over time. In engineering systems requiring very stable high frequency oscillators, a lot of R&D goes into developing compensating circuitry that will keep an oscillators frequency "on the mark". How close you want it "on the mark" will, of course, depend on various factors, like theoretical limitations, how much money you're willing to spend ( the big one :-) ), etc. I don't know what is done in cmos clock oscillators in this regard, but I would be surprised if they are "highly" temperature compensated.

Aha - so my machine that's been losing time all summer may start to gain time in winter? :)

This is sort of analogous to my piano, where I use a "Humidistat" to keep the strings from stretching/shrinking during damp/dry seasons.