, it might look something like the graph shown in Figure 5-14. Each additional measurement (+ or -) is added to the graph at the right. A value of zero means that for that measure- ment, the offset between the signals was measured as zero. Time error max|TE| 15 ns Figure 5-14 Graph Showing cTE, dTE, and max|TE This figure also includes several statistical derivations of TE, the main one being max|TE|, which is defined as the maximum absolute value of the time error observed over the course of the measure- ment. The following sections explain these measures and concepts. Refer to ITU-T G.810 and G.8260 to get more details about the mathematical models of timing signals and TE. 5.2.1 Maximum Absolute Time Error The maximum absolute time error, written as max|TE, is the maximum TE value that the meas- ured clock has produced during a test measurement. This is a single value, expressed in units of seconds or fractions thereof, and represents the TE value that lies furthest away from the reference. Note that although the TE itself can be positive or negative, the max|TE| is taken as an absolute value; hence, the signed measured value is always written as a positive number. In Figure 5-14, the max|TE is measured as 50 ns. 5.2.1 Time Interval Error The time interval error (TIE) is the measure of the change in the TE over an observation interval. Recall that the TE itself is the phase error of the measured clock as compared to the reference clock. So, the change in the TE, or the TIE, is the difference between the TE values of a specific observa- tion interval. The observation interval, also referred to as T (tau), is a time interval that is generally fixed before the start of a measurement test. The TE is measured and recorded at the beginning of the test and after each observation interval time has passed; and the difference between the corresponding time error values gives the TIE for that observation interval. As an example, assuming an observation interval consists of k cycle times of a clock, the calcula- tions for