Re: "..a 21.9:9 aspect ratio."
Since ratios are supposed to always be Integers (or at least that's what my A Level Maths teacher taught me), the correct ratio is 219:90.
However, if you are going to use decimal places, then all ratios should be relative to 1 so your 21.9:9 is in fact 2.43:1 (to two decimal places). Cinema screens are 1.85:1 or 2.39:1, and HD TVs are 1.78:1 It's much easier to compare stuff if you stick to ONE standard method. YES, I'm getting my coat already! :-)