[ewanm89]

Okay so the article is wrong about some points. We have evidence for both IIII and IV notation in classic roman archeological finds. The obvious example is the entrance fee doors around the colliseum in Rome, they're are engraved with numbers, in both forms of notation.

Seriously I figured they used abacus for everything they just figured out the notation to write it down in at the end some would convert to the if notation while others would not.

[TorKlingberg]

It seems the subtractive notation was used for engravings, where keeping it short was important and nobody was going to do calculations with the numbers anyway.

[wklauss]

> We have evidence for both IIII and IV notation in classic roman archeological finds.

The article doesn't say subtractive notation was not used in classic roman times, it says only that it was rare.

[jacobolus]

> Seriously I figured they used abacus for everything they just figured out the notation to write it down in at the end some would convert to the if notation while others would not.

Yes, this is exactly right, and should be at the top of this discussion thread. Romans (like the Greeks, the Babylonians, and others in the ancient world) did their calculations using a counting board. Roman numerals were only used for recording the final answers.

“When a Roman wished to settle accounts with someone, he would use the expression vocare aliquem ad calculos - ‘to call them to the pebbles.’” http://mathforum.org/library/drmath/view/57572.html

Our words calculate, calculus, calculator, etc. all come from the Latin word for the pebbles they used as counting-board tokens.