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Type I clocks belong to the Option 1 hierarchy based on 2048kbit/s. The maximum peak-to-peak amplitude at each frequency is taken from Table 13 of G.812. This is a translation of the MTIE mask defined in Table 9 of G.812, using the relationship between tone frequency, *f*, and observation interval, tauτ, of *f* = 1/ pi.tau πτ .

The lowest tone frequency specified in Table 13 of G.812 is 0.000012Hz (12µHz), which has a period of over 23 hours. However, the longest observation interval specified in the MTIE mask (Figure 3) is 10000s, equivalent to a tone frequency of 0.000032Hz (32µHz). Therefore it is sufficient to make 32µHz the lowest tone frequency in the test.

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Type II and III clocks belong to the Option 2 hierarchy based on 1544kbit/s. The maximum peak-to-peak amplitude at each frequency is taken from Table 14 of G.812. This is a translation of the MTIE mask defined in Table 10 of G.812, using the relationship between tone frequency, *f*, and observation interval, tauτ, of *f* = 1/ 2.5tau 5τ . This is slightly different to the relationship used for the Option 1 hierarchy.

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