Domain Time II uses clock slewing (adjusting the rate at which a machine believes that
time passes) both to improve overall accuracy, and to prevent corrections from making
the clock appear to go backward in time. Clock slewing is only supported on NT Class
Use slewing to improve long-term clock accuracy
Domain Time II attempts to reduce the frequency of time checks by adjusting the
internal clock rate of each machine. Domain Time II collects statistics over time
to determine if a particular machine is consistently faster or slower than its
server. Domain Time II slowly changes the internal clock rate to bring it into conformity with the
rest of the network. When system clocks are all running at about the same
speed, the number of time checks and amount of each correction can be significantly
reduced. This behavior is enabled by default, but may be disabled on a per-machine
When you first install Domain Time II, you won't see much difference between two machines,
one with slewing enabled and the other not. But as Domain Time II gets to know the
machine over a period of days or weeks, the machine with slewing enabled will need
to check the time less and less often. After Domain Time II has been running for
several weeks, it's not unusual to see the average check interval cut by more than
half. You will obtain best results after the Domain Time II Master has finished
"learning," since the master's clock jitter is necessarily propagated to the rest
of the network. But even with a wobbly master, the other servers will learn the
limits of your particular network and optimize network traffic automatically. And of
course, between checks your clocks will be closer to unity, too; and the amount of
each eventual correction will be smaller than if slewing were not enabled.
Use slewing for small backward or forward time adjustments
When Domain Time II is adjusting a machine's clock to match an external source, the
machine can either be ahead of or behind the external source. Domain time can either
adjust the clock immediately (called "stepping" the clock) or adjust it slowly over
a period of time (called "slewing" the clock).
Domain Time II uses clock slewing to temporarily slow down or speed up the machine instead
of just changing the time. Using clock slewing this way helps ensure that no running process
will ever see the clock move backward in time. The adjustment is invisible to the
foreground user; Domain Time II spreads the speed change across time, and only the clock
accumulation counter is affected, not the machine's processing speed.
Domain Time II uses slewing by default, but this behavior may be disabled.