Re: My Computer Drifts!
On 20220604 02:25:26, David J Taylor via groups.io wrote:
On 04/06/2022 08:31, Dirk wrote:
My configuration here involves a Linux router that does a lot of other work and a largish set of PCs around the house, mostly here in the computer room. They range from PLCs to a rather hypertrophied gaming machine use for multiple VMs, development, and the like. (Visual Studio is THE preeminent game in the known universe.)
When speaking of accuracy you have to deal with a pot load of different entry points for errors. The ones NTP monitors and considers in its design are delay, offset, and jitter. NTP, as embodied in the canonical Univ of U of Delaware version as amended up to date, measures the path delay in such a way as to get a reasonable estimate of path delays to multiple sources. The path to and the path from the server may be slightly different. You can see that in the offset value. NTP makes a best estimate for time and publishes the time offsets. It also passes this information along to the consumers. Offset here varies from -5.3ms to 5.9ms. The chosen clock and the secondary are coming in at + and - 2 ms. The chosen clock is .NIST.. The secondary clock is .GPS. I could setup a pure GPS configuration here if I hooked up the PPS from my Trimble to the router. But, it's not broke so I don't fix it. The final figure, jitter, gives a good estimate of the link quality between the consumer and the hosts. The two good ones are coming in at under 6 ms of jitter. All these numbers vary with time of day. For my current needs this is good enough. If I needed better I'd have to go to a formal PPS hookup. (None of the USB crap, either. They do look like fun to play with, though.)
For my main PC I am using a very old tool I have had for a long time. Mr. Horsley created an open sores partial implementation of ntp that I use to tweak my PC's clock in 1ms steps - since at least early XP days through today. I have it logging clock corrections. Most are 0 ms with the occasional 1ms correction. I ran Symmetricom's ntp for awhile. But I went back to Tom's tool. It ain't broke and I have a much older view on the urgency to make perfect than I used to have.
(I am one of the persons responsible for the GPS phase 2B satellite segment's extremely accurate intentional inaccuracy for whatever worth that may be.)
If ntp accuracy is insufficient at least one more protocol exists
that refines to microseconds or finer. It is/was used by radio
astronomers to get them in the ballpark.