VMS Help PASCAL, Predeclared Routines, Arithmetic, ARCTAN  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  The ARCTAN function returns  a  real  value  that  expresses  in
  radians the arctangent of the specified parameter.

  Syntax:

     ARCTAN( x )

  The parameter 'x' can be an integer or REAL type.