I like this approach. One small wrinkle (especially when talking about precision) is that many fonts optimise for the pixel grid at small type sizes, so 15px vs

I like this approach. One small wrinkle (especially when talking about precision) is that many fonts optimise for the pixel grid at small type sizes, so 15px vs 16px vs 17px can look like completely different typefaces (on non-retina screens). Sometimes, this kind of variation in character can impact the look of the page more than imprecision over viewport–type size ratios – the latter is usually just a matter of having variable width margins, which is rarely a problem. I think using absolute px sizes gives designers a feeling of control for this reason. Then again, forcing a preferred glyph set by setting a hard px size is (a) only applicable if you're using fairly small type sizes, and (b) probably gives you a false sense of security anyway – it's all going to change the moment someone zooms their browser, or uses a weird OS, or any number of other things. I think I mostly agree with the author.