its a L shaped scale or ruler used to measure perpendicularity, alignment and parallelness among certain intruments. Its used almost daily for calibrating the positions of instruments to make sure they are straight and thus carry out perfect job execution.
This equation describes all the points on the unit sphere. There is an infinite number of solutions. Some quick integer solutions would be (1,0,0) and (0,1,0) and (0,0,1) which are the one the axes.