[manasecret]

The measurement is generally very accurate. But all kinds of delays have to be taken in account when taking that accurate measurement from deep down in the cpu somewhere and displaying it to the screen. You have to contend with all kinds of threads running at the same time, all trying to take up the CPU time, and consider that the little system clock display is not considered a high priority thread. Then you have the delays inherent in sending the value to RAM and then back out the RAM through to the video card or whatever traversing is needed, finally on to the screen. There are so many variables there, that while possible to get a super accurate clock display, it's just not worth the trouble.