Rant warning: the contents of this post could sound like something produced by UKIP. I wish to make it clear that I do not in any way support or endorse that political party. In fact it gives me the creeps.
Once upon a time, the signs for a steep hill on British roads displayed the gradient in a simple, easy-to-understand form. If the hill went up, say, one yard for every three yards forward it said '1 in 3'. Then some bureaucrat came along and decided that it would be a good idea to state the slope as a percentage. So now the sign for (say) a 1 in 10 slope says 10% (I think).
That 'I think' is because the percentage-based slope is so unnatural. There are two ways we conventionally measure slopes. Either on X/Y coordiates (as in 1 in 4) or using degrees - say at a 15° angle. We don't measure them in percentages. It's easy to visualize a 1 in 3 slope, or a 30 degree angle. Much less obvious what a 33.333 recurring percent slope is. And what's a 100% slope? It sounds like it should be straight up vertically, but I assume it's really 1 in 1 or 45 degrees.
It's widely reported that the general public is very bad at understanding percentages. That is sad, and ought to be rectified - but it's true. So why, in heavens name, make a street sign, something that a driver is supposed to pick up and react to in seconds, in a format that most people struggle with, and a format that is never conventionally used to measure an amount of slope? It's madness. Madness, I say!
Photo from Freefoto.com