Why do we measure? Signals must fit into the system that carries them, if not, then the situation shown in Figure 4.1 will arise. All transmission systems, whatever the medium or method used, have maximum signal limits. Where signals exceed this maximum, distortion of the signal and the information it carries will occur. The form of distortion will depend on the system and how it has been misused, and the effect on the signal will depend on its resilience.