Caution, Steep Grade

I never understood those highway signs that describe hills in terms of grade, expressed in percent. Angles, which is what I assumed the grade measured, should be expressed in degrees -- or, perhaps, as a ratio of rise over run. What's with this percent business?

Now I know. Grade is just rise as a percent of run -- that is, rise over run multiplied by 100.

Source: http://www.1728.com/gradient.htm