I have therefore made TimeSync display a message that clock adjustment is going on so that users do not panic. A couple of reasons for this. At this time the operating system is naturally not in control. On booting up the machine again the operating system reads the current time from the RTC and keeps the time till the machine is switched off again. On top of this the RTC might drift due to the characteristics of the crystal clock.
Crystals are very sensitive to temperature and when the PC is off the temperature tends to be lower.
The drift of the crystal could be considerable if the PC is not off over longer periods. If you have a connection to the Internet there are public NTP servers . Even your access point to the Internet may have NTP installed. Network Time Protocol is an Internet standard for very accurate time keeping. Please ask your friendly ISP and complain if he does not have an NTP server.