VMS Help Sys Parameters, CLOCK_INTERVAL  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    (VAX only) CLOCK_INTERVAL sets the number of microseconds between
    the hardware interval timer clock interrupts. It has no effect on
    processors that have implemented only the subset interval clock
    registers.

    This special parameter is used by Compaq and is subject to
    change. Do not change this parameter unless Compaq recommends
    that you do so.