Continuous time-domain electrical signal that only has a finite number of possible values I have recently started learning DSP and the book that I am reading challenges the readers to find a:


  continuous time-domain electrical signal that only has a finite number
  of amplitude values


I obviously could not think of an example and hence I am here. 

Please suggest an example of continuous electrical signal that takes only finite number of discrete values ?
Well, a DC signal for sure.

Other than that, there is probably more context from the book required (especially about the assumptions).