# Reference Data

These are reusable reasoning aids, not a bag of numbers to recite.

| File | Use |
| --- | --- |
| [Estimation anchor ledger](estimation-anchor-ledger.md) | Order-of-magnitude anchors, source routes, derivations, and freshness rules for guesstimates |
| [Metric and equation reference](metric-and-equation-reference.md) | Denominator-safe metric definitions, business equations, and decision use |
| [RCA evidence taxonomy](rca-evidence-taxonomy.md) | Evidence sources, diagnostic cuts, causal traps, and discriminating tests |
| [Product-design edge-case checklist](product-design-edge-case-checklist.md) | Inclusion, safety, lifecycle, channel, and operating edges that generic design answers miss |

## Rules

1. State the population, geography, time period, unit, and inclusion rule.
2. Prefer a range to fake precision.
3. Label a number as a sourced fact, derived value, interview assumption, or
   sensitivity bound.
4. Recalculate derived values when the underlying source changes.
5. In a timed interview, explain the model before reaching for an anchor.
6. A remembered anchor may initialize an estimate; triangulation must still test
   it.