How to make an Altoids Tin Pocket Abacus

Here's how you can make a pocket abacus from an empty Altoids tin: "This abacus will have 9 columns (9 digits). You can calculate up to 9,999,999.99 if you use decimals, or up to 999,999,999 if you only use whole numbers. For this you will need to poke 9 holes, to string 9 wires."

(Thanks Albert)