calculator-displayer is a variable defined in `calculator.el'.
Its value is
(std 110)

A displayer specification for numerical values.
This is the displayer used to show all numbers in an expression. Result
values will be displayed according to the first element of

The displayer is a symbol, a string or an expression. A symbol should
be the name of a one-argument function, a string is used with a single
argument and an expression will be evaluated with the variable `num'
bound to whatever should be displayed. If it is a function symbol, it
should be able to handle special symbol arguments, currently `left' and
`right' which will be sent by special keys to modify display parameters
associated with the displayer function (for example to change the number
of digits displayed).

An exception to the above is the case of the list (std C [G]) where C is
a character and G is an optional boolean, in this case the
`calculator-standard-displayer' function will be used with these as

You can customize this variable.