Life drawing Reseach

I heard that 7 heads equals the hight of a average person, with a bit of research I found it's somewhere between 7-9 I found this handy chart showing it for all the stages till adulthood on proportions 

I continued researching farer and found this site  http://pennycow.blogspot.co.uk/2011/08/matter-of-proportion.html?m=1 

It covers lots about how to get the proportions rights and how to messure.