Question? If I am framing a basement with 2x4's, I have chalked the lines on the floor, marked and secured the floor plates and now am ready to place the top plates. I plum up to place my top plate but all I get is air space, either because I fell between two joist or because I am parrallel to to the joist. How do I determine where my end point is so that my top plate falls directly over my bottom plate. Thank you very very much in advance.