I just got my bf% tested at OSU, with calipers, Bod Pod, and underwater, and the bod pod and underwater were MUCH higher then the calipers, which seems to be the same for everyone I've talked to.
Ok, you say you want to lose 10%, and the comment was made "10% of 18% rather then 18%-1-%". Getting down to 16.2% from 18% in a month is a pretty light goal, I would say. Just eat clean and exercise.
However, if you were, like the title of your thread implied, meaning you want to shed 10% bf, then just give it up and don't hurt yourself, because if you did this in your 'gym class', it means you're in high school. And high schoolers DON'T NEED TO BE FUCKING WITH DNP!!!! I don't care how informed or whatever you think you are, this is a time when losing bf will be the easiest for you, so don't worry about drugs unless they're mild, like an eca.
I'll bet with a highschool dude's metabolism you could keep everything the same, take xenadrine, and shed the 1.8% in two weeks.