Source variation is a valuable metric within the Timebeat application. This metric allows you to gain confidence in your sources of UTC and the level of synchronisation that Timebeat provides. Source variance is sometimes referred to as Traceability which is important for many reasons, not the least for some timing regulations.
It is important to note that you will only log Source Variation metrics if your system is configured to use MSSA (Multis Source Synchronisation Algorithm), this is where you have multiple sources of UTC each configured to a different domain (if PTP). If you are using a mix of PTP, PPS, and NTP then this metric will be available but you may not have the optimal configuration for clock sync - the Timebeat support team may be able to assist in enhancing this if desired.
Source variance is a metric that starts to be recorded when you have 2 or more active sources of UTC reporting.
The above image represents 3 active sources of UTC. From the graph, it is easy to see that 2 of the sources agree with each other more than the other (the bottom line on the graph is the outlier).
In simple terms, the source variance is the range between the top line on the graph above and the bottom line.
If we compare the graph above and the graph below we will be able to see that the variance corresponds.
The benefit of understanding this is that it can provide a check and balance on your sources of UTC. Put simply it can very effectively show when you have an errant or deviating source of UTC.
At Timebeat we recommend 3 sources of UTC whilst using the MSSA configuration as this provides ground breaking source resilience. The reason being Timebeat will always synchronise against the median source (the middle line) and as such if one source starts to deviate even by great amounts, Timebeat will continue to sync to a reliable source and the overall sync accuracy is unaffected.