org-table-formula-constants

org-table-formula-constants is a variable defined in `org-table.el'.
Its value is

nil

Documentation:
Alist with constant names and values, for use in table formulas.
The car of each element is a name of a constant, without the `$' before it.
The cdr is the value as a string. For example, if you'd like to use the
speed of light in a formula, you would configure

(setq org-table-formula-constants '(("c" . "299792458.")))

and then use it in an equation like `$1*$c'.

Constants can also be defined on a per-file basis using a line like

#+CONSTANTS: c=299792458. pi=3.14 eps=2.4e-6

You can customize this variable.