DatumNest
Build signed mechanical dimension chains, compare worst-case and RSS variation, and run a repeatable Monte Carlo screen from iPhone or iPad.
Focused field tools
Write the closed dimensional relationship before assigning signs or tolerances.
Confirm each contributor is measured from the same functional references used by assembly.
Use positive and negative coefficients to preserve the physical direction of closure.
Sum absolute tolerance effects when every extreme must remain acceptable.
Use root-sum-square only when independence and distribution assumptions are defensible.
A stated ±3 sigma range is not interchangeable with a drawing limit without process evidence.
DatumNest is an engineering screening and communication tool. Confirm datum schemes, geometric effects, correlations, distribution assumptions, process capability, units, and acceptance criteria with qualified design and quality personnel.