You only have to know two PCA commands to do simple PC sampling.
    PC sampling is typically the first kind of data you want to
    gather. It provides a good overview of where your program is
    spending the most time. To do PC sampling you must:

    1. Compile your sources with the "/DEBUG" qualifier;

       This puts all the necessary symbolic information PCA needs
       into the object file.

    2. The following steps specifies the PCA Collector as your
       program's "debugger":

        i Link your program with the "/DEBUG" qualifier;

       ii Define the logical name LIB$DEBUG as PCA$COLLECTOR;

    3. Run your program;

    4. Enter the "GO" command at the PCAC> prompt.

       The Collector will transfer control to your program just like
       the debugger does, and will store the data in a data file
       named your-image-name.PCA.

    5. Enter "PCA your-image-name" at DCL level after your program
       has finished.

       This invokes the Analyzer.

    6. Enter the "NEXT" command at the PCAA> prompt

       This will give you an annotated source listing and point to
       the line where your program spent the most time. Continue
       issuing NEXT commmands and "walk" from the most significant
       line ("hot spot") to the next one, and so on. See Traverse_
       Commands for more information on moving from "hot-spot to
       hot-spot".