Treadmill "% Grade"?

Okay, Here’s a stupid Question for you all.
In this post i will be referring to the “7 Cardio Drills That Don’t Suck” Article.

If you look onto the article (Linked here: 7 Cardio Drills That Don't Suck)
Number 3, It refers to the Bruce Protocol and talks about grade of a treadmill. (10-28 in regard to %)
How does one set a % grade on a treadmill??
I know a % grade is not the same as the .5 increments a treadmill has.

Please help out!

Thanks in advance!

As far as I know, grade is basically the incline. If necessary, I’d adjust the suggested specific numbers to whatever allows you to increase it 1-2 “points” per level through the workout, even if it’s:
level 1) 5%
level 2) 7%
level 3) 9%
level 4) 11%
level 5) 13%
level 6) 15%

You’re still getting to the general idea of the protocol.