http://web.archive.org/web/20130128031622/http://www.bccmp.com/mazzetti/pagine/MA10xx.html National's MA10xx Alarm Clock Modules

If it does not concern to you the ability of a clock to be able to place itself perhaps but mainly around running accuracy, would be a DS3231 (temperature-compensated RTC) http://www.maxim-ic.com/datasheet/index.mvp/id/4627 something for you. Even if one does not use clock functionality, it is still an oscillator, which knows any clock praying documents. The thing runs here for months, without a noticeable deviation to a radio clock.



http://eu.st.com/stonline/prodpres/memory/selector/mpge_a40.htm Timekeeper(R) SRAM Thats a SRAM + RTC + BATTERY

http://www.pdixtal.com/ Oscillateur pour environnements sévères Série OC8037 de Precision Devices

48MHz Crystal

http://www.atmel.com/dyn/resources/prod_documents/doc397c496b2072e.pdf TEMIC ANM032 How to use a Third overtone crystal with a 80C51 Family Microcontroller

Murata XRCGB48M000F0L00R0, $0,35

      X1      X2
      |       |
      |       |
      |      1M
      |       |
     15pf    15pf
      |       |
     GND     GND


Days in a year: http://en.wikipedia.org/wiki/Year#Calendar_year
Simplified answer: about 365.2425 days. The ancient Romans approximated
this as 365.25 days, handled with a 365-day calendar plus 1 leap day
added every 4 years, the so-called Julian calendar. The discrepancy
built up over the centuries til it was adjusted in the 18th century
(depending on where you were), by skipping 11 days and changing the leap
year algorithm slightly, giving the Gregorian calendar now in use.

Try the Unix command "cal 9 1752" or see:

Months in a year: I think this is supposed to be the one everyone gets
right, i.e. 12, but of course I'm suspicious. I've heard that the one
thing that's really stayed constant is 7, the number of days in a week.

Hours in a day: varies slightly, but the period of the earth's rotation
(sidereal day) is about 23.9344699 hours (23h 56m 4.09 sec). The solar
day is slightly longer (averages just a tiny bit over 24h) but its
length varies with the season:

Seconds in a minute: 60 but sometimes there is a forward or backward
leap second. http://en.wikipedia.org/wiki/Leap_second

Quartz - Crystals - Oscillators:


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M--j: 23 novembre, 2014