VMS Help FORTRAN, Intrinsic Procedures, ACOS  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  ACOS (number)

  A function that returns the arc cosine of the argument in radians.
  The absolute value of the argument must be less than or equal to 1.

  +------+---------+----------+------------+-------------+
  | Args | Generic | Specific |  Argument  | Result Type |
  +------+---------+----------+------------+-------------+
  |  1   | ACOS    | ACOS     | REAL*4     | REAL*4      |
  |      |         | DACOS    | REAL*8     | REAL*8      |
  |      |         | QACOS    | REAL*16    | REAL*16     |
  +------+---------+----------+------------+-------------+