cks, in more detail in the following chapters. The following sections explains the different states of the clock as depicted in Figure 3-10 and out- line what those states mean and the clock behavior during the time they are in that state. Warming Up Oscillator characteristics such as accuracy, frequency stability, temperature sensitivity, and other characteristics are defined when the oscillator is in a steady state of operation. Before it reaches that steady state, it is in a state known as warm-up, where the temperature, airflow, and power supply voltage have not yet stabilized. During this time, a standalone reference clock may signal to downstream clocks that its accuracy is likely to be degraded, and that no other clocks should use its signal as a reference. As described in the preceding section on oscillators, the stability can improve even after the warm-up time has ex- pired. The length of time an oscillator takes to reach its steady state is called the warm-up time. When the warm-up time has expired, then the clock may signal the quality based on the technology of its oscillator. On the other hand, a clock that takes input from a reference source may immediately signal the quality of the reference to downstream slaves, rather than the quality of its own (still warming up) oscillator. Free-Running Typically, when equipment powers up, it does not have any reference clock signal or traceability to a reference clock. Free-running is a clock mode where the local oscillator runs without any refer- ence clock as input to guide it. To be in this condition, the local clock either never had a connection to a reference clock or has lost the reference clock for an extended duration. So, the clock runs free without any attempt to control or steer it with an external control circuit (the temperature compensa- tion circuitry of a TCXO is still functioning even in free-running clocks). Note that the quality of the frequency from a free-running clock (there is no phase alignment) is dir- ectly correlated with the qualit