In message <20040125183335.B30359_at_gamplex.bde.org>, Bruce Evans writes: >relevant sysctl so that they are all as accurate as possible. For the >i8254 clock, the best possible is 0.5 / 1193182 seconds or about 0.5 >ppm, since fractional frequencies can't be set. 0.5 ppm is a good >practical accuracy to aim for since the frequencies of all clocks on >all my machines drift with the temperature by about +- 2 ppm every >day. It is indeed worth noting that while quartz crystals has just the right combination of properties to be our only affordable timekeeping device of any precision (in fact: no other crystals have the right combination of properties), it is even better at measuring temperature. For anybody venturing into timekeeping I would really urge you to start by reading John. R Vig's tutorial "Introduction to Quartz Frequency Standards" before you attempt anything: http://www.ieee-uffc.org/fcmain.asp?view=review Also, you have to realize that you need _three_ identically good oscillators for measuring anything, unless you have a GPS receiver with precision PPS output. It's an expensive hobby, but very rewarding, for people with an inclination to physics: http://www.leapsecond.com/ -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk_at_FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.Received on Sun Jan 25 2004 - 00:21:02 UTC
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