For entirely boring reasons, I was looking at the table of hat size 
conversions appropriately located at http://hatsizes.com/

I used a simple regression to reverse engineer the equation from this 
table, and it seems to be:

US_size = circumference_inches / pi + 0.037

So, the division by pi makes sense to me, but does anyone have any idea 
where the + 0.037 comes from?

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