Click here to purchase the entire book in PDF format. M-H curve So far, the description of the behaviour of the tape has assumed that we apply a magnetic field to the tape, and then apply a different magnetic field (for example, as if we were going to try to erase it). However, it's usually more useful to apply a magnetic field, and then leave the tape alone. That way, the signal that we applied remains on the tape. In this case, the curve to describe the behaviour of the tape has already been shown (or at least half of it was...) in Figure 6.58. If we assume that the tape behaves the same in the opposite polarity (and it does...) then the complete curve will look like Figure 6.62. Figure 6.62: $M-H$ curve for magnetic tape. Note the two nearly-linear areas on the curve. One important thing to notice about this curve is that there are two nearly-linear parts on it. This is an important piece of information for the next section.