Ageing of vintage quartz crystals, do they slow down?

[Wade]

I notice that most of my modest collection of vintage LED watches run slow several seconds slow a week. And then for those for which I replaced the quartz crystal (with a modern one) - they run faster than what was replaced. Have you all found a similar pattern that the vintage quartz crystals slow down as they age? I'm not too anal about it, just curious.

[rewolf]

A year ago I reactivated my 1984 Casio that used to run dead on back then (I remember I had trimmed it to 1s/month) but now it runs fast several s/week.

[retroleds]

It is a well known phenomena that quartz crystals tend to slow to a degree and then stabilize until such time as they fail. When purchasing quartz crystals, look for those with the lowest "ageing" numbers,10pppm or lower, and the widest temperature range(although, accuracy may be quite off at the end of their range). The oldest,early crystals were cut and ground pieces of particular quartz'(primarily silicon dioxide), the modern ones are generally lab grown and formed in sheets and cut or formed right on the electrodes that make the electrical connections to them. Back in the day many manufacturers burned-in(ran) their crystals for a few days to get rid of some of the initiall decline, so their watches could be adjusted before leaving the factory, to a fairly high accuracy. Others explained that their watches needed to be adjust a few times during the first few months to bring them into the claimed accuracy. And others just figured it was close enough. Many of us set our watches a minute fast if it tends to run slow and figure when it bothers us enough we will re-set it. Even if you set it with a timing machine, once on someones arm it is probably 15-20 degrees(Fahrenheitt) warmer, which will tend to throw the timing off marginally.

[rewolf]

Talking about crystal temperature characteristic: the curve is inverse parabolic, with its maximum (=nominal frequency) at 25°C(77°F). Any deviation (higher or lower) leads to lower frequency.

[Wade]

Many of us set our watches a minute fast if it tends to run slow and figure when it bothers us enough we will re-set it.

That's precisely what I do. Part of the fun for me is periodically setting/re-setting my watches.

[retroleds]

Part of the fun for me is periodically setting/re-setting my watches.

You are a sick man.....keep coming back, you are in good company.