code: def setPhysicalDimension(self, edfsignal, physical_dimension):
          
          if edfsignal < 0 or edfsignal > self.n_channels:
              raise ChannelDoesNotExist(edfsignal)
          self.channels[edfsignal]['dimension'] = physical_dimension
          self.update_header()
docs: Sets the physical dimension of signal edfsignal ("uV", "BPM", "mA", "Degr.", etc.)
  
          :param edfsignal: int
          :param physical_dimension: str
  
          Notes
          -----
          This function is recommended for every signal and can be called only after opening a file in writemode and before the first sample write action.