Andrew Loomis and his proportional scale for the male figure.
Notice where the discrepancy between the number of "heads" occurs.
For the most part the change occurs in the length of the legs.
The anatomical mid point always remains the pubic synthesis. It is easy to see here why the idealistic approach to depicting the figure became the baseline for the artistic cannon for so long.
Breaking the figure into an easily understandable and communicable "base 8" allows for quick and easily relatable proportional studies.
The fact remains that very few humans fall into this norm. Any set of proportions has to be understood to exist as a means to begin, a starting point. When working from the figure your drawing must always be informed by what you see before you.
Let the proportional guidelines help you but do not allow yourself to be dictated by them.