riddle concerning playground

How was the Manhattan project scientist able to perform a difficult calculation while relaxing at a playground?

He told the children that they must hold onto the handrails of the slide as they climb the steps.  By making this slide rule, he was then able to perform the calculation.

>>3
Well, that must be true, since I'll turn 25 in March. But then again, a quick Google search revealed that this "riddle" only returns this thread, so that's in all likelihood pure bullshit. Nice try, though.