Distance – Maximum dimension of surface or axis The Surface Start Point on the X-Axis distance from the reference Start Point on the Y-Axis distance from the reference End Point on the X-Axis distance from the reference End Point on the Y-Axis distance from the reference Distance between Points DIN, ISO, ASTM, ASME, or Federal G-Series Measurement Specifications [plain text] Perpendicularity is a fairly common symbol that requires the referenced surface or line to be perpendicular or 90° from a datum surface or line. Perpendicularity can reference a 2D line, but more commonly it describes the orientation of one surface plane perpendicular to another datum plane.