Variables and functions and formulae have numerous applications.
It is, for example, possible that the parametric value of a geometrical object
is calculated with the help of a variable or function or formulae and then can
be used for the construction.
It is also possible to save such a relation, parameter -
(variable,function,formula). Any modification of the variable
causes that the parameter(s) depending on it are calculated anew. And, the
construction will change.