If you selected an analog input subdevice, you probably noticed
      that the output of tut1 is an unsigned
      number, for example between 0
      and 65535 for a 16 bit analog input. Comedi
      samples are unsigned, with 0 representing the
      lowest voltage of the ADC, and a hardware-dependent maximum
      value representing the highest voltage.  Comedi compensates
      for anything else the manual for your device says (for example,
      many boards represent bipolar analog input voltages as signed
      integers).  However, you probably prefer to have this number
      translated to a voltage.  Naturally, as a good programmer, your
      first question is: “How do I do this in a
      device-independent manner?”
    
      The functions
      comedi_to_physical, comedi_to_phys,
      comedi_from_physical and comedi_from_phys
      are used to convert between Comedi's integer data and floating point numbers corresponding
      to physical values (voltages, etc.).