In sci.electronics.basics wrote:
A long time ago, I regularly had good luck by substituting crystals
taken from watches, but when I tried the crystals from computer clocks
in some of those watches, their accuracy would worsen considerably.
And crystals I bought from parts suppliers were so bad that I switched
to getting my crystals from stick-on clocks for cars

A National Semiconductor note for one of their clock chips mentioned
that common crystals varied from 1-100 ppm accuracy per year (~30 secs.
to almost 1 hour), the worst by far being those sealed with solder, the
best sealed in glass or without heat.

Got any pictures to examplify the solder vs glass seal ?