nder is the long-term variation of the meas- ured clock compared to the reference clock. The ITU-T G.810 standard defines jitter as phase vari- ation with a rate of change greater than or equal to 10 Hz, whereas it defines wander as phase vari- ation with a rate of change less than 10 Hz. In other words, slower-moving, low-frequency jitter (less than 10 Hz) is called wander. One analogy is that of a driver behind the wheel of a car driving along a straight road across a fea- tureless plain. To keep within the lane, the driver typically "corrects" the steering wheel with very short-term variations in the steering input and force (unconsciously, drivers do these corrections many times per second). This is to correct the "jitter" of the car moving around within the lane. But now imagine that the road is gently turning to the right and the driver is beginning to impact a little more force on the steering wheel in that direction to affect the turn. This is an analogy for wander. The jitter is the short-term variance trying to take you out of your lane, but the long-term direction being steered is wander. The preceding sections explained that MTIE and TDEV are metrics that can be used to quantify the timing characteristics of clocks. Therefore, it is no surprise that the timing characteristics of these clocks based on the noise performance (specifically noise generation) have been specified by ITU-T in terms of MTIE and TDEV masks. These definitions are spread across numerous ITU-T specifica- tions, such as G.811, G.812, G.813, and G.8262. Chapter 8 covers these specifications in more detail. Because these metrics are SO important, any timing test equipment used to measure the quality of clocks needs to be able to generate MTIE and TDEV graphs as output. The results on these graphs are then compared to one of the masks from the relevant ITU-T recommendation. However, it is im- perative that the engineer uses the correct mask to compare the measured results against. For example, if the engineer is measuring SyncE output