A compatibility engine can be deterministic and still be dishonest. The obvious failure is a wrong calculation. The subtler failure is unjustified certainty: turning a blank birth time into noon, allowing a nickname to change a result, or comparing an Hour Branch that was never calculated.
Source: [Dev.to](https://dev.to/baziclarity/testing-a-two-chart-compatibility-engine-without-inventing-missing-data-3e38)