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--- comfilepi:set_date_and_time [2026/03/31 04:00] – [Drift Compensation] mfranklin
+++ comfilepi:set_date_and_time [2026/04/05 23:54] (current) – [System Clock Compensation] mfranklin
@@ Line 14: / Line 14: @@
 ===== Drift Compensation =====
+There are two clocks that have the potential to drift:  The RTC and the operating system's system clock.  Both will drift independently, so the Linux operating system provides utilities to configure compensation for both.
+==== RTC Drift Compensation ====
 If you notice the RTC drifting over time, and the drift is consistent and predictable, it is possible to configure the OS to compensate for the drift using the following procedure:
-  - With Internet time synchronization disabled, run <html><code>sudo ntpdate pool.ntp.org</code></html> to manually synchronize the system time to an Internet time server.
+  - With Internet time synchronization disabled, but with an Internet connection, run <html><code>sudo ntpdate pool.ntp.org</code></html> to manually synchronize the system time to an Internet time server.
   - Run <html><code>sudo hwclock --systohc --utc --update-drift</code></html> to synchronize the RTC with the system time, and to ensure the ''/etc/adjtime'' records the last calibration time.
   - Power off the panel PC for a few days; the longer the better.
@@ Line 45: / Line 50: @@
 </code>
-Reboot, and after booting, the device should have its system time synchronized with the RTC, and adjusted to compensate for the RTC's drift.  Confirm with the ''date'' command.
+Reboot, and after booting, the ComfilePi should have its system time synchronized with the RTC, and adjusted to compensate for the RTC's drift.  Confirm with the ''date'' command.
+==== System Clock Compensation ====
+After configuring the RTC's drift compensation, the system clock's drift compensation can be configured.  For that we need [[https://manpages.debian.org/trixie/adjtimex/adjtimexconfig.8.en.html|adjtimexconfig]].
+Run the following commands in a terminal.
+<code>
+sudo apt update
+sudo apt install adjtimex
+sudo adjtimexconfig
+sudo systemctl enable adjtimex.service
+</code>
+The ''adjustimexconfig'' command will measure the amount of drift the system clock has relative to the RTC, save it to ///etc/default/adjtimex// and the //adjtimex.service// will load that at every boot to compensate.
 [[comfilepi:index|ComfilePi - Industrial Raspberry Pi Panel PC]]

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