Jtdylktuy

I configured a system displaying some emergency data, and it needs to change information once a day, at a certain time (8 am). In the last year, the system clock was about 7 minutes fast. How can I synchronize it without hooking up the system to the internet?

My alarm clock was able to receive a signal from the atom clock, can I use that same signal every now and then? I mean, checking once per week would already be plenty.

First, let me agree that "yeah, this happens." 7 minutes' error over a year is about a half a minute per month, or about a second per day - similar to any decent digital watch. There is no reason to expect a PC's clock to be any more accurate than that; they use similar hardware.

"can I use that same signal [from NIST's atomic clock] every now and then?" You can, but while ordinary desk and wall clocks that use that signal are cheap, versions with computer interfaces start at a couple hundred for a used one.

But if you have a real budget (and for a critical task, you should), look for a "WWVB receiver". (WWVB is the radio station in the US that the so-called "atomic clocks" use.)

If you're outside the continental US, many other countries have their own time standard signal stations, and receivers for them will be sold in those countries. See: https://en.wikipedia.org/wiki/Radio_clock#List_of_radio_time_signal_stations

Or look for a GPS receiver with a data connection, or at the high end, a "GPS disciplined clock". GPS can provide reliable time that, with a little extra software (available as freeware), your computer can set itself to. (You may have to add a serial port to your computer.)

Right now (January 2019) you can find GPS-sourced time receivers with "disciplined" oscillators (which means they will continue to provide reliable time even when GPS signals are not received) on eBay for under USD 200. Or you can use a simple USB GPS receiver like the GlobalSat BU-353-S4 (under USD 100). Here is information on using one of those:
http://www.k5pa.com/Ham%20Radio/Downloads/Using%20GPS%20to%20Set%20Computer%20Time.pdf There are many similar devices.

If you're trying to do this on the cheap, an older consumer GPS unit with a serial output (like a Garmin GPS III or V) will also work. But I have to say that using such a gadget for an important part of a critical task ("displaying emergency data") would be what I'd call a "hacky" solution. These units are intended to run on internal batteries (4xAA), but they do have a connection for a cable that can both provide DC power (which you could tap off of the computer's internal power supply) and gives you the serial data you want. Trouble is that if power ever dies someone will have to manually push the button to turn the GPS back on after power returns. Besides, the receivers in older GPS units won't be nearly as good as recent ones. More recent consumer GPS units with map displays, intended for e.g. driving or hiking, generally don't have data outputs.

Depending on your location and situation, one or the other (GPS or WWVB) might give you better reception. GPS requires putting an antenna where it has a fairly clear view of the sky, although recent receivers work pretty well inside residential wood frame buildings. (A metal roof will likely be a problem. If you're deep inside a steel frame building, forget it.) Geographically speaking, GPS works anywhere in the world.

WWVB works more or less well in the continental US, depending on how close you are to Fort Collins, Colorado, and what obstacles lie between you and there. In difficult situations you may have to get the antenna either outside, or near a window on a side of your building that doesn't face away from Colorado.

Another option: Do you at least have an old-fashioned phone line available? Dial-up internet services still exist (though who knows for how long?). You could connect to the 'net every so often and resync your time with NTP while you were connected.

As suggested by MZB in the first comment, there's also the option of using a dial-up time data service. Unlike dial-up internet service, these are generally free to use, except for the cost of the phone calls - which should be short and fairly infrequent. You'll need a POTS (plain old telephone service) phone line and a modem.

Make a google search for gps+windows+time+sync

https://www.google.com/search?client=firefox-b&q=gps+windows+time+sync

You will find several services or apps that you can connect via GPS and maintain the correct time with among the search results.

Also check out this older post

https://serverfault.com/questions/448617/adjusting-windows-time-drift-without-internet-on-windows-server-2003

Quote:

GPS is the typical solution for machines that need time sync but have
no external network connectivity. There are various software
applications, both free and commercial, that can use a GPS receiver to
sync the system time (search for "gps windows time sync" and you'll
find a number of them). If you'd prefer an embedded device you can
also find a number of devices that package up the entire GPS receiver
into an Ethernet-attachable NTP server.

I don't have personal experience with either solution so I'm not going
to make any specific recommendations. There are quite a number of
offerings in both spaces out there, though.