A combination square is a multi-use measuring instrument which is primarily used for ensuring the integrity of a 90° angle, measuring a 45° angle, measuring the center of a circular object, find depth, and simple distance measurements.
It can also be used to determine level and plumb using its spirit level vial.

Before using a combination square, one must first be familiar with the structure and terminology of the square itself. A combination square consists of a rue-type blade attached to a handle. The handle is composed of two parts, a shoulder and an anvil. The shoulder is placed at an angle of 45° between itself and the blade. It is therefore used for the measurement and layout of miters. The anvil is placed at a 90° angle between itself and the blade. The handle contains an adjustable knob which allows it to move freely horizontally along the edge of the ruler so that it may be tailored towards any size job. Additionally contained within the head of the handle is a scriber used for marking measurements and a vial which may be used for measuring plumb and level.