Picture Hanging Tip: Use an L-Square LevelApril 14, 2013
Here’s a tip for hanging a picture on a wall that you need to get perfectly straight: use an L-Square that has a bubble level gauge on it, such as this model made by Swanson. Hang the picture on the wire, place the l-square on one corner, adjust the frame angle until the bubble is centered, and then remove the l-square.
Another cheaper method that works fairly well is to take a thin strip of wood, and drive a nail into one end. Place the nail on one corner of the picture so that the wood balances on the edge, and use the wood strip like a plumb line to line up the edge of the frame. It can easily fall off, especially if the nail is too long or short, or the wood strip may be bent or not perfectly straight, and give a bad reading. A piece of plastic or metal might work better than wood.