Normally signals flip from one logic state to another. The time it takes the signal to move between states is the transition time , where the time is measured between 10% and 90% of the signal levels. Delays within the logic elements result in a propagation (pulse) delay , where the time is measured between 50% of the input signal and 50% of the output response. Definitions of the transition time and propagation delay are shown in figure 7.5.
Figure 7.5: The transition time of the input and output signals, and the propagation delay through a gate.