King of the Mountains: Tour of Britain does gradient on The Struggle

We watched the Tour of Britain bike race come up The Struggle from Ambleside onto Kirkstone. The gradient gets up to 20%. Physicists love gradient but we normally do up divided by across, in other words, how far up you go for every one you go along. It turns out that road gradient is not the same. The old 1 in 5 that I remember from childhood means 1 up for 4 along the slope of the road - in other words, along the hypotenuse. 1 divided by 5 is 0.2, or the new 20%.