Engineering reference data: GD&T symbols, modifiers and ISO 1302 surface-roughness grades as verified Unicode tables

Three small, machine-readable reference tables for mechanical drawings, in CSV and JSON, where every claim is checkable by a script included with the dataset. gdt-symbols — 14 geometric characteristics: symbol, Unicode codepoint, category, whether a datum reference is required, and status in ASME Y14.5-2018 against ISO 1101. The two standards do not carry the same set, and the difference is recorded per row rather than flattened. gdt-modifiers — 15 material-condition and drafting modifiers: MMC, LMC, projected tolerance zone, counterbore, countersink, depth, all-around and the rest. surface-roughness-grades — the ISO 1302 N-grade series N1–N12 with preferred Ra values. CSV is the source of truth; the JSON twins are generated and checked for agreement. verify.py re-derives every Unicode codepoint from the Unicode Character Database and fails if any claim drifts — the version of record for this deposit checks 29 codepoints and 12 N-grades against UCD 16.0.0. Most GD&T and surface-finish charts published on the web are images, transcribed from one another, with no indication of which standard revision a row belongs to or where a codepoint came from. This dataset is the opposite: plain text, one fact per column, documented columns, and a verifier anyone can run. Column definitions are in COLUMNS.md. Released under CC0 1.0.