I did a lot of anthropometrics (as a profession) and for the average 25 year old european population the one-eigth rule seems to hold independent from body size, a one-six would be prepuberty. The one-eigth rule also holds for the european standard (wo)man. You must buy the template if you want to construct car seats (joke), so I can post no picture of it. If you put a female p4 figure in front of the measurements or create a flat plane and texture it with the jpg above, and then put the plane in the middle of the figure you will see that the p4 almost exactly matches. Vickies head actually is to small. Test it out.