Section 11,2: ACOS

 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      |
 |      |see note | QACOS    | REAL*16    | REAL*16     |
 +------+---------+----------+------------+-------------+

 NOTE: QACOS is not available in DEC Fortran.