Putting together a cargo box for my FJ60 I needed to drill as-near-as possible holes perpendicular to the plywood surface. I did a couple of test holes which came through at unacceptable angles. Not having easy access to a drill press the idea of attaching a post level to the drill came to mind, and it works well enough for what I've been doing. With the plywood lying flat, using the post level on the drill, and carefully watching the pair of individual horizontal levels the holes can be drilled to an acceptable perpendicular degree. I'm using a 14v Milwaukee drill in this case and the post level attaches flatly. I'm sure there will be plenty of other drills which will not work. YMMV, etc.
Just wanted to pass this along in the event someone else may find it useful.