Distance – Nominal distance between parallel planes {Axis or surface} Largest dimension of the plane being measured Start Point on the X-Axis distance from the reference Start Point on the Y-Axis distance from the reference Start Point on the Z-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 End Point on the Z-Axis distance from the reference Distance between points DIN, ISO, ASTM, ASME, or Federal G-Series Measurement Specifications [plain text] Parallelism is a fairly common symbol that requires the referenced surface or line to be parallel to a datum surface or line. Parallelism can reference a 2D line, but more commonly it describes the orientation of one surface plane parallel to another datum plane.