this is a rather curious old machine from 1972. this unit is 110v
      mains only and offers 8 digit, four function plus constant operation.
      when powered up, the 8 digits are always displays with no zero
      suppression.
      the machine does not have the ability to display and error, so that an
      overflow will display the result mod 10^8, ie the lowest 8 digits.
      dividing by zero causes the unit to hang where the lowest digits flicker
      and spin round indefinitely. the clear button stops this.