SYSE.30:4.4 - Compare independent repetitions and explain differences

When the receiving use needs reproducibility, repeat from the identified inputs in a fresh execution. Where the claim includes transfer between builders, use the relevant independent builder or environment, not just a second invocation on the same dirty worker.

Compare the specified output bytes, commonly through a suitable cryptographic digest followed by a useful difference inspection when they differ. Change one suspected influence at a time when that can discriminate the cause. Explain the variation before accepting an equivalence claim.

For incidental build timestamps, prefer removing them from the specified artifact or deriving a needed date from the named source. Retain actual execution time in separate build evidence when it is needed. A tool-specific fixed-date mechanism works only where the selected tool supports it; changing a clock globally can affect behavior that depends on elapsed time. Rebuild and compare after the repair.

A matching pair is bounded evidence, not proof against every future environment. If a dependency, toolchain or output requirement changes, qualify the affected build again. Preserve a useful partial result: “the build runs from these inputs, but archive order remains uncontrolled” is more informative than “reproducible” with an unexplained exception.