Even with a steady hand, it's easy for the tool to waver. TOH master carpenter Norm Abram drills perfectly perpendicular holes using a wood block as a guide. Cut one end of the scrap square. Using a combination square, draw a line perpendicular to the cut end. Hold the block against the wall and let the penciled line direct the drill bit at the target. Remove the block after the hole is under way. Once the bit is partially set, it should drive straight.