In Fig. 4.3 we present a basic example of a 1-event (or 1-finger) classification sequence, which is the most basic type of physical-layer classification. The initial part of that process is detection of course. The detection portion just happens to be a two-step ascending staircase in the figure. It could well be a descending staircase, and maybe consist of two, three, four or even more steps. It could also be, say, two steps ascending followed by two steps descending, and so on. As mentioned earlier, detection can also be done either with current sources or voltage sources. We see that many possibilities for detection exist within the framework of the IEEE standard.