The value returned by the clock function must be divided by the
    value of the CLK_TCK, as defined in the standard header file
    <time.h>, to obtain the time in seconds.

    The type clock_t is defined in the <time.h> header file as
    follows:

    typedef long int clock_t;

    Only the accumulated times for child processes running a C main
    program or a program that calls VAXC$CRTL_INIT or DECC$CRTL_INIT
    are included.

    A typical usage of the clock function is to call it after a
    program does its initial setup, and then again after the program
    executes the code to be timed. Then subtract the two values to
    give elapsed CPU time.