deskthority

http://kevintwomey.com/calculators.html

Pretty interesting photos of mechanical calculators including the keys used on them.

Nice photos indeed!

Could someone explain why some of the calculators have multiple number sets from 0-9?

They are probably mechanical ones where you would press the rightmost column for 1's, the second column for 10's etc, and then you'd press the operator (+,-,*,/) and repeat.