The method he describes is quite easy: draw a line right down the middle
of the pelvic bone. Then check
if half the body's on the left, the other half on the right.
If not, you need to compensate of your figure will fall (in real life).
For the figure I drew I did this by raising his right arm and putting his
left foot nearer to the central line. Note that the book doesn't weigh anything
because it's floating.
What you might notice from such a sketch, like the one the left, is the sense of balance
the figure shows.
I found a nice method for drawing balanced figures in an anatomy book I own by
Jenö Barcsay. I don't know if there's a English version of the book,
it's originally in Hungarian and I found it in Dutch.