The clock returns
an approximation of time used.
The time used so far;
the number of seconds.
The standard allows for arbitrary
values at the start;
subtract the value returned from clock
to get maximum.
Note that the time can wrap around.
On several implementations,
the value returned by clock also includes
the times of any waited-for children.
(separate) information about the caller
and its children, may be preferable.
clock was implemented on top of times.
Found poem (erasure) from the Linux man pages