Granite Square Ruler

The granite square functions as a primary geometric reference standard, with its principal metrological application being the precise evaluation of three fundamental geometric tolerances:
1. Perpendicularity assessment: Quantitative evaluation of the angular deviation between the machine tool spindle axis, slide motion direction, and worktable reference plane—typically performed in accordance with ISO 1101 and verified via optical alignment or dial indicator probing;
2. Parallelism inspection: Determination of parallelism error between two nominally parallel surfaces (e.g., guide rail faces or opposing workpiece features), leveraging the square’s mutually calibrated opposing planes as traceable datum references;
3. Flatness calibration: Use of the square’s optically finished, thermally stable granite surface—as certified to flatness ≤0.5 μm over 100 mm (per JJG 700–2018)—as a high-accuracy reference plane for flatness measurement via stylus profilometry or interferometric methods.