/sys$common/syshlp/helplib.hlb FORTRAN, Intrinsic Procedures, RAN  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  RAN (seed)

  A function that returns a different REAL*4 number between 0.0
  (inclusive) and 1.0 (exclusive) each time it is invoked.  The
  argument must be an INTEGER*4 variable or array element.  For best
  results, you should initialize the argument to a large, odd value
  before invoking RAN the first time.  To generate different sets of
  random values, initialize the seed to a different value on each
  run.  Do not modify the seed during a run.