VMS Help BASIC, /CHECK  *Conan The Librarian (sorry for the slow response - running on an old VAX)

   The /CHECK qualifier causes the compiler to  generate  code  to  test  for
   arithmetic overflow and for array references outside array boundaries when
   the program executes.

   The format of the /CHECK qualifier is as follows:

      /[NO]CHECK[=({[NO]BOUNDS                              },...)]
                   {[NO]OVERFLOW[=([NO]INTEGER,[NO]DECIMAL)]}
                   {ALL                                     }
                   {NONE                                    }

   where:

      BOUNDS         Checks array subscripts to ensure that they  are  within
                     array boundaries specified by the program.

      OVERFLOW       Enables the detection of arithmetic overflow for integer
                     and packed decimal operations.

   The /CHECK qualifier specifies that both OVERFLOW and BOUNDS checking  are
   performed.    The   /NOCHECK  qualifier  specifies  that  no  checking  is
   performed.  If you specify /CHECK=OVERFLOW, overflow checking  is  enabled
   for  both  integers  and  packed  decimal  numbers.  Similarly, specifying
   /CHECK=NOOVERFLOW disables overflow checking for both types of numbers.

   Specifying /CHECK=NOBOUNDS means that your program  is  smaller  and  runs
   faster.   However, no error is signaled for an array reference outside the
   bounds of an array.   This  means  that  the  program  may  get  a  memory
   management  or access violation error at run time.  Therefore, this option
   should be used only for programs that have been  thoroughly  debugged  and
   whose execution time is critical.

   The default is /NOCHECK.