As discussed earlier, the entire magnetization system precesses at approximately the Larmor frequency w0. However, because of small (Hz-per-MHz, or part-per-million) frequency shifts arising from the presence of different chemical groups in the sample, some magnetization components are rotating slightly faster than w0; others, somewhat slower. Obviously, one wants to encompass all these frequencies with the recorded signal. This is done by specifying both the offset frequency (which defines the center of the observed frequency range), and the sweep width (which describes the breadth of the range and will be discussed further in the next section). If it is changed to a lower value, the spectrum appears shifted to the left.