Straightness

The Straightness at U+23E4 is a technical symbol used to denote the geometric tolerance of straightness. It belongs to the Miscellaneous Technical block and is a printable symbol rather than a letter or punctuation mark. Its main real-world use is in engineering drawings and geometric dimensioning and tolerancing, where it identifies a straightness requirement for a line element, axis, or derived median line. In a feature control frame, ⏤ may be followed by a tolerance value to say how much a surface line or axis may deviate from perfect straight form. It is most common in mechanical design, manufacturing inspection, machining, and quality-control documentation that follows GD&T standards such as ASME Y14.5 or ISO GPS practice. A shaft, rail, guide surface, or machined edge might receive a straightness tolerance so inspectors know whether to check form with a coordinate-measuring machine, dial indicator setup, or straightedge-based method. Because the symbol is specialized, many general fonts do not make it visually prominent or may substitute a plain horizontal mark. In technical documents, it should not be confused with a minus sign, dash, or overbar, since its meaning depends on GD&T notation rather than ordinary arithmetic or typography.