Never mind that a size 8 in the US is different from a size 8 in the UK, Denmark, Hong Kong or Lithuania.
Why is a guy’s size 8 a different length from woman’s size 8? Who came up with shoe sizes and what were they thinking anyway? Apart from making it easier to get shoes that fit.
The same person who made women’s clothing sizes different from men’s? And women’s hat sizes different from men’s? And women’s underwear sizes different from men’s? And women’s coat sizes different from men’s? And…
Charles Brannock apparently bears some responsibility.
Possibly coming up with your own unique way of measuring shoe sizes was part of the patent process for his ingenious doohickey.
From your link, we find this article on shoe size which seems to contain the details you want.