e up of three values: Grandmaster clock class: The clockClass value in the range of 0-255 (8 bits) indicates the traceability to a time source, meaning how well the master is synchronized to a source of time. As an example, in many profiles the value 6 indicates traceability to a PRTC, but the allowed values can vary depending on the profile. Grandmaster clock accuracy: The clockAccuracy metric is based on the quality of the source of time on the grandmaster in the timeSource attribute below (8 bits). For example, traceability to GPS would result in a clockAccuracy value of 0x21 = time is accurate to within 100 ns. Values are enumerated in Table 6 of IEEE 1588-2008. Grandmaster offset scaled log variance: The offsetScaledLogVariance is an estimate of the stability of the GM (16 bits). This is an estimate of the variations of the clock and thus the pre- cision of the timestamps (see section 7.6.3 of IEEE 1588-2008 for a math-heavy treatment). For example, the value of 0x4E5D indicates a GM connected and locked to a PRTC, but the value can vary between 0x0000 and 0xFFFF. Perhaps the most important field in the Announce message is clockClass. In some PTP profiles, as well as IEEE 1588 PTP default profiles, a clock class of 6 indicates a clock that is synchronized to a PRTC. If the clock loses the connection to the PRTC and goes into holdover, the clockClass value will change to a higher number indicating the loss to traceability to a source of time. More details on clock classes are included in the following section "Telecom Profiles." Note that the Announce message is not forwarded by a boundary clock. It is used to update the datasets (see the upcoming section "PTP Datasets") on the BC and new Announce messages are created to advertise service to downstream slave ports. This means some values can be updated (one example is stepsRemoved that will be increased by +1 to indicate another additional PTP hop back to the grandmaster). The next section examines how the Announce message is used. 7.3.1 Best Master Clock Alg