Library /sys$common/syshlp/pca$help.hlb SET, PC_SAMPLING, Qualifiers, /INTERVAL  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /INTERVAL:n

    Specifies the sampling interval in milliseconds. The value of n
    must be at least 10 milliseconds and at most 60,000 milliseconds.
    Because the granularity of the system clock is 10 milliseconds,
    you should use a multiple of 10. The default sampling interval is
    10 milliseconds; therefore, you can use the /INTERVAL:n qualifier
    only to specify a slower sampling rate.