Squareness -

• The measured angular misalignment (error) between the axes of two nominally perpendicular carriages. Because of other errors, the axes are determined via both definition and measurement by standards documents.
• In practice, it applies to the calculated two dimensional angular misalignment between the measured axis of a carriage and a corresponding axis of a reference coordinate system. The reference coordinate system is associated with another carriage or object. Usually measured in arcseconds for a machine tool.