I am probably overlooking something extremely simple, but it has me stopped dead in my tracks. I'm trying to make a sketch plane perpendicular to a line, as if it was balancing on the line's endpoint.  For the life of me, I can't figure out how to do it.  Anybody have any helpful tips or tricks?  Or a brick to hit me in the head with for not being able to do something that's probably incredibly simple? I put a picture to help, though I'm not sure how helpful it will be.