As all clocks, even more, the time of your PC is not always exact. So, it is necessary to update it sometimes.
When you are on line on the Internet, you click on the icon of Atom Time, and the clock of your PC is adjusted to an atomic clock, somewhere in the world...
The difference with french hour (and other countries, of course) is respected.
To be at the very exact hour !
At the beginning, I used Atom Time, but it is now a shareware. Net Date is as practical. Excepted at the installation, wher you have to type ann address whre to find the hour. The avalaible address are on the page Public NTP Secondary (stratum 2) Time Servers.