I am trying to use ps to determine the amount of memory in bytes
that my program is using.  In SysV this is done with ps -l and the
SZ option lists the size (in pages) of the swappable process's
image in main memory.

How is this achieved in BSD?  

Also I see rss, rsz, tsiz, and vsz
but the man pages are most unclear (technically) what each parameter
is.  It would be most helpful if someone could explain these to me
or point me in the direction to find out.

Thanks

Roger