Library /sys$common/syshlp/pca$help.hlb SET, VPC_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 the least 10 milliseconds and at the most 60,000
    milliseconds. Because the granularity of the system clock is 10
    milliseconds, use a multiple of 10. The default sampling interval
    is 10 milliseconds; therefore, you can use the /INTERVAL:n
    qualifier only to specify a longer sampling interval.