erence in expected timing characteristicsbased on the oscillator quality. For example, a primary reference clock or primary reference source (PRC/PRS), based on a cesium atomic reference, is expected to provide better accuracy and stability when compared to a clock based on a stratum 3E OCXO oscillator. Chapter 3 thoroughly discussed these different classes of oscillator, SO now it is time to define some metrics to categorize these qualities more formally. 5.2.1 Constant Versus Dynamic Time Error Constant time error (cTE) is the mean of the TE values that have been measured. The TE mean is calculated by averaging measurements over either some fixed time period (say 1000 seconds) or the whole measurement period. When calculated over all the TE measurements, cTE represents an av- erage offset from the reference clock as a single value. Figure 5-14 showed this previously, where the cTE is shown as a line on the graph at +15 ns. Because it measures an average difference from the reference clock, cTE is a good measure of the accuracy of a clock. Dynamic time error (dTE) is the variation of TE over a certain time interval (you may remember, the variation of TE is also measured by TIE). Additionally, the variation of TE over a longer time period is known as wander, SO the dTE is effectively a representation of wander. Figure 5-14 showed this previously, where the dTE represents the difference between the minimum and max- imum TE during the measurement. Another way to think about it is that dTE is a measure of the sta- bility of the clock. These two metrics are very commonly used to define timing performance, SO they are important concepts to understand. Normally, dTE is further statistically analyzed using MTIE and TDEV; and the next section details the derivations of those two metrics. 5.2.1 Maximum Time Interval Error As you read in the "Time Interval Error" section, TIE measures the change in time error over an ob- servation interval, and the TIE is measured as the difference between the TE at the start and end of th