[time-nuts] Most accurate small crystal

Jim Palfreyman jim77742 at gmail.com
Thu May 27 04:22:18 UTC 2010

Hi All,

I have a RSA SecurID device which I use to log in to my work's VPN. For
those of you not familiar with these, they show you a 6 digit number that
you use (combined with a PIN) to log in. This number changes every minute.
The changing of this number lines up with the servers at the other end and,
as I understand it, they do take into account gradual drift. These devices
have a limited programmed lifetime of three years as well. So the internal
clock on one of these needs to be decent.

I have timed the accuracy of this internal clock and have found it to be
pretty good so far. 17 days ago it was ticking over at 21.8 sec past the
minute and a quick visual inspection today and it was still *very* close to
that. I will confirm it properly tonight.

Now this device travels around with me, like a wristwatch, but is not on my
person. It is usually in my laptop bag. So it is subject to quite varying

So it's been nearly 3 weeks and this device has barely changed 0.1 to 0.2
secs tops. Now that's not bad compared to digital watches.

I presume it has a quartz crystal in it, obviously no oven, but my question

What is the best crystal you can get on the market today that would work in
a watch type device with very little power available? What's the best
accuracy that can be expected?

I know straight out of the factory they can be pretty spot on (as my Casio G
Shock was) but it has aged markedly and now gains a couple of seconds a
week. So what is the best we can expect long term too?


Jim Palfreyman

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