Nospam said:
Good day,
The time on my machine keeps being 10 mn earlier than the real time
even though I reinitialize it once in awhile.
Does anyone know where that comes from ?
Thank you
At the hardware level, a quartz crystal only has so much long term
accuracy. On a digital watch, there would be a trimmer capacitor
that you could twist, to get exactly 32768 Hz from the oscillator.
But that would only last for a while, and it would drift off again.
As far as I know, there is no provision to do that on a computer.
It is also unlikely that the computer oscillator design, has
any temperature compensation, so as the room temperature changes,
so will the 32768Hz operating frequency.
Time pieces can be kept calibrated, by using the NTP protocol over
the Internet. NTP allows passing time information from one
computer to another. The appropriate Stratum of time piece, is tied
to at least one of the NTP servers, so that the time is traceable to
the rest of the world. Local software keeps track of drift rate,
and by contacting the NTP server at regular intervals, can keep
time accurate to at least the seconds level.
If you want your own fairly good time reference, you can get that
via GPS. The 1 PPS output of devices like this, can be down to
the 1 microsecond level. When your computer has one of these,
the computer can be used to calibrate other computers you own
that don't have GPS receivers. Using the very same NTP protocols.
http://www.symmttm.com/products_blt_gps_pci2u.asp
Paul
