The ideal measure, according to Bringhurst, is between 20em and 40em. Of course many factors may influence this number. For instance, line-height: the higher the line-height, the wider a measure can be. Which makes sense. When there's more space between each line of text, it's much easier to find the next line than when all lines are cramped together. This could result in the idea that we should use the vw unit to define line-height: the wider the viewport, the higher the line-height should be. As we saw, [using vw for line-height is unusable on small screens(https://vasilis.nl/nerd/code/line-height/vw/). This page uses vmax instead of vw. It works much better. Very big line-heights on wide screens, and not too small on medium sized screens. But on smaller screens, like the iPhone 4, the line-height is way too small. So no, this is not usable as well.
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