No, I am not talking about having a mid-life crises and blowing the kid’s college fund on fast watches, loose cars and expensive women (or men for the few ladies present).
I am talking about the affects of age on watches and how it will alter the performance, specifically in quartz movements.
Aging of a quartz oscillator is defined as “the systematic change in frequency with time due to internal changes in the oscillator.” Aging is caused primarily by mass transfer to or from the resonator’s surface due to absorption or de-absorption of contamination, stress relief in the mounting structure of the crystal, changes in the oscillators circuitry and, possibly, changes in the quartz material.
Aging can result is a positive or negative rate change, depending on the cause of the aging, sometimes if there are two aging factors at work a combination of the two will result in the rate change first rising then falling, or vice versa.Because the typical quartz crystal used in a watch is thin, about 1 million atomic layers, the absorption/de-absorption of contaminants equivalent to the mass of one atomic layer of quartz will change the frequency about 1 part per million (PPM). In order to achieve low aging, you can see that crystal units must be fabricated in ultra-clean ultra-high vacuum environments, and then hermetically sealed.
Aging rates of typical commercially available crystal oscillators ranged from 5 - 10 PPM for inexpensive crystal oscillators to 0.5 to 2 PPM for higher grade thermally compensated crystal oscillators.
A 5 to 10 PPM/year change in rate means a movement’s rate will change 0.5 to 1 second per year.
All quartz are not equal......