calculator-operators is a variable defined in `calculator.el'.
Its value is

The calculator operators, each a list with:

1. The key that is bound to for this operation (usually a string);

2. The displayed symbol for this function;

3. The function symbol, or a form that uses the variables `X' and `Y',
(if it is a binary operator), `TX' and `TY' (truncated integer
versions), `DX' (converted to radians if degrees mode is on), `D'
(function for converting radians to degrees if deg mode is on), `L'
(list of saved values), `F' (function for recursive iteration calls)
and evaluates to the function value -- these variables are capital;

4. The function's arity, optional, one of: 2 => binary, -1 => prefix
unary, +1 => postfix unary, 0 => a 0-arg operator func (note that
using such a function replaces the currently entered number, if any),
non-number (the default) => postfix or prefix as determined by

5. The function's precedence -- should be in the range of 1 (lowest) to
9 (highest) (optional, defaults to 1);

It it possible have a unary prefix version of a binary operator if it
comes later in this list. If the list begins with the symbol 'nobind,
then no key binding will take place -- this is only useful for predefined

Use `calculator-user-operators' to add operators to this list, see its
documentation for an example.