Every archer needs a bow square. It’s just one of those tools that archers should have on hand to help out with a number of tasks.Also called a T-square because of its shape, a bow square is a measuring device that can be clipped to the bow string. There will be measurement lines on both the vertical and horizontal bars of the square. On some squares the long ruler is rounded, on others it’s flat. Compound archers tend to prefer the rounded squares, while recurve archers opt for the flat ones.Recurve archers are going to use a square in multiple ways. They will use it to set their nocking points. They will clamp the square to the string, set the ruler on the bow’s arrow rest or shelf and then refer to the vertical ruler that’s against the string to set their nocking points. There will be a mark letting the archer know where dead center or "zero" is located, and then lines measured in sixteenth inches above and below that zero.Recurve archers shooting ILF or Formula bows also will use a square to check tiller measurements for their top and bottom limbs. The tiller measurement is taken from the belly of the limb, just above or below the riser - depending on whether you’re measuring top or bottom limb - to the string on a level plane.The tiller measurement affects how the bow sits in your hand. If the tiller is not set correctly – to your shooting style and preferences – then the bow might lean forward or backwards. Tiller also makes sure both limbs work in unison. Some archers will want the tiller measurements to be the same between the limbs and the string, while others might like one to be longer than the other. Tiller adjustments are made by turning limb bolts in or out.Arguably the most frequent use of a bow square for a recurve archer will be to measure brace height. Brace height is the distance from the deepest part – throat – of the grip and the bow string. For consistent shooting, that distance must always be the same, yet it has the potential to change almost every day.Every time you string and unstring your bow, you should measure the brace height. As you shoot a bow repeatedly, you also should periodically measure brace height.If you measure it and it’s a bit longer than normal, unstring the bow and take a few twists out of the string. If it’s below normal, add some twists to the string.Compound archers will want a bow square primarily during initial setup to help position their nocking point. As mentioned, compound archers often prefer the rounded square because the cylindrical, long ruler imitates an arrow shaft. The "shaft" sits on the arrow rest, and the other end is clipped to the string. There are lines on the vertical ruler indicating where nocking points – usually D-loop material on compound bows– should be placed to surround the arrow.Some archers like to nock their arrows a bit above dead center, and so they can use a bow square to set their nocking points at a specific measurement above the center.