/sys$common/syshlp/helplib.hlb PASCAL, Predeclared Routines, Misc, ZERO  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  The ZERO function  returns  data,  whose  type  depends  on  the
  context  of  the function call, that sets any variable (except a
  file variable) to its binary zero.

  If you attempt to use the ZERO function  to  initialize  a  file
  variable, an error occurs.  Do not specify a parameter list when
  you call the ZERO function.