Example 1x, after breakpoint from this article.
640px / (33,3vw x 1x) = 1920px = 120em
I don't understand this expression.
I thought that 1vw = 1% so
640px / 33,3% = 213,12px
and it's different than 1920px.
How it was calculated?
I know that 33.3 is a result of 100/3 but the expression in my opinion is incorrect. The only way to get 1920 in this case is multiply 640 by 3.
Article author here. Math with vw units (and percentages!) can get a bit confusing... 33.3vw, as you say, is equal to 33.3% of the width of viewport, aka ⅓ of the viewport width. 640px ÷ ⅓ = 640px × 3 = 1920px.