Observations in the time and in the frequency domain; the representations and transformations of identical phenomena
The mathematical representation of signals is created according to the content of practical tasks, observation opportunities and the nature of computation. Identifications between the two representations are performed by transformations.
The tram timetable in the picture shows the minutes left until the arrival of the next tram in two different ways. For processing either information we need a reference system: a watch. Arrival times and frequencies are calculated by a simple transformation.