A try-square is a woodworking

Woodworking

Woodworking is the process of building, making or carving something using wood.-History:Along with stone, mud, and animal parts, wood was one of the first materials worked by early humans. Microwear analysis of the Mousterian stone tools used by the Neanderthals show that many were used to work wood...

 or a metal working tool

Tool

A tool is a device that can be used to produce an item or achieve a task, but that is not consumed in the process. Informally the word is also used to describe a procedure or process with a specific purpose. Tools that are used in particular fields or activities may have different designations such...

 used for marking and measuring a piece of wood

Wood

Wood is a hard, fibrous tissue found in many trees. It has been used for hundreds of thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers embedded in a matrix of lignin which resists compression...

. The square refers to the tool's primary use of measuring the accuracy of a right angle (90

90

Year 90 was a common year starting on Friday of the Julian calendar. At the time, it was known as the Year of the Consulship of Augustus and Nerva...

 degrees

Degree (angle)

A degree , usually denoted by ° , is a measurement of plane angle, representing 1⁄360 of a full rotation; one degree is equivalent to π/180 radians...

); to try a surface is to check its straightness or correspondence to an adjoining surface. A piece of wood that is rectangular

Rectangle

In Euclidean plane geometry, a rectangle is any quadrilateral with four right angles. The term "oblong" is occasionally used to refer to a non-square rectangle...

, flat, and has all edges (faces, sides, and ends) 90 degrees is called four square.