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
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.