assumption-registry-builderlisted

# Assumption Registry Builder ## When to use Use this skill when a model is complete and needs to be documented for handover, sign-off, or recurring use. Trigger it when a client or reviewer asks "where do your assumptions come from?", when a model needs to be formally approved before a capital allocation decision, when the model will be updated by multiple people over time, or when a business case requires a formal assumption sign-off log. It converts a working model into a fully documented, auditable asset. ## What it does Produces a structured assumption register: a dedicated Assumptions tab listing every material assumption in the model, with columns for assumption name, category, base value, source and rationale, Bull and Bear values, sensitivity rank (impact on key output), and owner. Includes the formula for computing sensitivity rank using Data Table outputs, and a flag system for assumptions that require active monitoring. ## Method 1. **Define what constitutes a "material assumption."** Not every input in a model needs to be in the assumption register. Material assumptions are: (a) inputs with high sensitivity (top 50% of the tornado chart), (b) inputs that are genuinely uncertain (not based on contractual or regulatory certainty), and (c) inputs that, if wrong, would change the recommendation or decision. Assumptions that are highly certain (e.g., statutory tax rates, known contract prices) still belong in the register but with a "Low" sensitivity rank and "Reg