For this user , accurate time is as simple as set it and forget it. Use Manual when you want to make a setting quickly. Use Once when you want to set the clock at a given time in the future, for example , to synchronize with another computer or system. Use Daily to maintain the clock accuracy at a reasonable level suitable for most users. Use Auto or Periodic when the accuracy of the system is crucial .
Auto is best when the desired level of accuracy is known and the time drift is relatively constant.
Periodic is appropriate for the most demanding environments when the clock must be kept within several seconds of standard time. If curious which mode to use , run ClockWatch in the Periodic mode for several days with an interval of 8 hrs. If the time difference between readings is relatively constant , then the Auto setting will probably be the best choice. The charts are useful for displaying the accuracy of the computer clock from readings over a time period. The Current Settings chart shows the difference in seconds between two successive readings, while the Clock Drift chart converts that difference into an accuracy reading as expressed in seconds of drift in clock time per 24 hour period.