Longest dimension in the surface of interest 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 x-y distance between points DIN, ISO, ASTM, ASME, or Federal G-Series Measurement Specifications [plain text] DIN, ISO, ASTM, ASME, or Federal G-Series Measurement Specifications [plain text] The minimum normal (perpendicular) distance between two parallel planes that fully contain a surface. Commonly, the two parallel planes may be constructed from the surface itself (in which the highest point and lowest point of the surface would be tangent to the two parallel planes), but a drawing may specify how the parallel planes should be constructed. Reference https://www.gdandtbasics.com/flatness/ Dimensioning and Tolerancing, Engineering Product Definition and Related Documentation Practices, ASME Y14.5-2018 https://www.asme.org/codes-standards/find-codes-standards/y14-5-dimensioning-tolerancing