If the trend of slave offset values calculated from the Sync Messages continues to increase or decrease over time, the local reference clock that increments the free-running counter is operating at a rate slightly slower or faster than the master reference. You can make a drift adjustment to the free-running counter by slightly increasing or decreasing the rate at which the counter increments. Doing so locks the frequency of the counter to the master reference (syntonization). Syntonization is the adjustment of a clock signal to match the frequency, but not necessarily the phase, of another clock signal.
Xn – X0 drift Adjustment = --------- Yn – Y0Where, n = number of sync interval separating time stamps (n>0).
Syntonization may also be achieved using SyncE.