Are you trying to keep the clocks synchronized to the right time, or are you trying to determine how accurate the real time clock actually is, without being synchronized?
If you simply want the times to be correct, there's a whole hierarchy of time servers that systems can sync to, and it's often built in to the OS, although you can usually specify time servers. Also, one system can synch to a time server, and then run its own time server for the other systems to sync to.
I have seen, and even used in the past, programs that not only sync to a standard time, but keep up with the local computer's drift from the last synchronization. I used this in the past when we had intermittent internet connections, so the program would correct the time by using the history of expected drift.
Usually, with either of these methods, if the correction is too much, it may assume an error and not do any correction at all.
Hopefully, I'm not totally missing your point. :)