That would, in fact, be an extremely steep slope. An 80% grade is steep enough that if you fall you do not stop until you reach the bottom.

http://www.foxnews.com/travel/2017/01/30/5-most-dangerous-sk...

More:

> In general, beginner slopes (green circle) are between 6% and 25%. Intermediate slopes (blue square) are between 25% and 40%. Difficult slopes (black diamond) are 40% and up. ...

https://en.wikipedia.org/wiki/Piste

That is very true. But my point still stands. People hear a percentage number and assume the max is 100.

Also generally with ski slopes the quoted gradient is some tiny portion of the run. Top to bottom the actual gradient is much less.

That is what an ice axe would be for, I presume.

The nice thing about it from an engineering perspective is that it doesn't distort at the ends of a scale.

A 10% grade over a horizontal distance of X will gain exactly twice as much height as a 5% grade over the same distance.

Percent grade is standard for road steepness at least in the US, e.g., 6% which requires effort for a loaded truck to climb.