Confirm you may share the drawing, photograph or scan the full sheet, symbols, labels and legend readable. Proprietary or confidential drawings, cropped legends and low-resolution scans are sent back; 30 per contributor at most, from a global base strongest in Southeast Asia, the United States and Europe. Drawing conventions follow the contributor's country and trade, adding notational variety a single-standard corpus lacks. No symbol or region annotations are included. Engineering drawings are commercially sensitive and rarely released for training, so diagram-understanding models learn from textbook figures and synthetic schematics; the permission requirement keeps the provenance documented. A test and fine-tuning corpus for symbol detection, legend parsing and diagram-to-structure extraction in construction, electrical and mechanical domains.