DatumChain Tolerance Stack

DatumChain is an offline tolerance-stack review bench for mechanical engineers, product designers, machinists, quality engineers, and inspectors. It turns a signed assembly dimension chain into a decision you can take into design review. Create a study with an acceptance window, then add every contributing feature in the same direction the drawing reads. Each link supports add or subtract direction, nominal size, and independent lower and upper tolerance. DatumChain calculates nominal closure, asymmetric worst-case limits, statistical RSS limits, and the remaining margin to each target boundary. The window map makes clearance immediately visible. Ranked contribution bars show which features consume the statistical tolerance budget, so attention goes to the dimension that actually drives the result. Duplicate a study to compare a proposed tolerance change without destroying the released baseline. Add measured mean and sample sigma for each feature to calculate Cp and Cpk beside the drawing limits. Status colors separate potential spread from centering risk. The engineering brief collects the target, nominal, worst case, RSS range, leading contributors, notes, and statistical assumptions for sharing through Apple's system share sheet. All projects and measurements stay in the app container on your device. DatumChain has no account, subscription, advertising, analytics, tracking, cloud sync, or developer-server upload. It is a one-time purchase. DatumChain is an engineering calculation aid, not a substitute for an approved drawing, dimensional-control plan, measurement-system analysis, process validation, statistical sampling plan, or qualified engineering judgment. RSS results assume independent centered processes and tolerance limits approximating ±3σ. Verify inputs, assumptions, standards, and manufacturing capability before release.