ManualCalibration < Support

---+Manual Calibration without =NTP=

This section describes how to calibrate the clock to an accuracy of order tenths of a second.  This procedure was found useful when =ntpd= was used on a [[KnownHardwareIssues][variable speed processor]] and upset the drift correction.  

---++ Linux

The aim is to calibrate the kernel frequency adjustment variable(s) stored in =/etc/adjtime=.  This following is a translation of [[https://www.linux-france.org/article/sys/heure/ch2.html#s-bref][Laurent Picouleau's page]]. Many thanks to Mike Cook for the above explanation and supplying this link.

The following steps are to be done as =root=.

   * Day 1
      * Set the CMOS clock to "approximately" UTC using the BIOS [[#FootNote1][(1)]].
      * Install =hwclock= and =adjtimex=
      * Run =hwclock --set --date="MM/DD/YY hh:mm:00" --utc= [[#FootNote2][(2)]] =--debug= on the fourth beep (radio, I presume) [[#FootNote3][(3)]]
   * Day 2
      * Run =hwclock --set --date="MM/DD/YY hh:mm:00" --utc --debug=
      * If the first value of the first line of =/etc/adjtime= is greater than 8 then 
         * run =adjtimex -u -c=
         * record the suggested value for "tick"
         * run =adjtimex -u -t suggested_value=
      * Run =adjtimex -u -l=/var/log/clocks.log=
   * Day 7
      * Run =adjtimex -u -l=/var/log/clocks.log=
      * Run =hwclock --set --date "MM/DD/YY hh:mm:00" --utc --debug=
      * Run =adjtimex -u -l=/var/log/clocks.log=
      * Run =hwclock --utc --hctosys=
      * Run =adjtimex -u -l=/var/log/clocks.log=
      * Run =adjtimex -u -c=22 -i=100=
      * Calculate the average of the 20 values given for "freq"
      * Run =adjtimex -u -f calculated_average=
      * Run =adjtimex -u -l=/var/log/clocks.log=

Phew!  Your clock system is now calibrated to your reference and will drift by about only one tenth of a second per day.


*Footnotes:*

#FootNote1 1. Or any other method

#FootNote2 2. Note care the date format: month/day/year

#FootNote3 3. Use local time, don't use GMT.


-- Users.ParkerJones - 25 Nov 2004
WebForm
NtpVersion	Select one...
OperatingSystem
OsVersion
This topic: Support > WebOrder > KnownHardwareIssues > ManualCalibration
Topic revision: r1 - 2004-11-25 - 15:40:00 - ParkerJones