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Signed-off-by: Christoph Schmatzler <christoph@schmatzler.com>

profiles/opencode/skill/spec-planner/references/estimation.md

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+# Estimation
+
+## Why Estimates Fail
+
+| Cause | Mitigation |
+|-------|------------|
+| Optimism bias | Use historical data, not gut |
+| Missing scope | List "obvious" tasks explicitly |
+| Integration blindness | Add 20-30% for glue code |
+| Unknown unknowns | Add buffer based on novelty |
+| Interruptions | Assume 60% focused time |
+
+## Estimation Techniques
+
+### Three-Point Estimation
+```
+Expected = (Optimistic + 4xMostLikely + Pessimistic) / 6
+```
+
+### Relative Sizing
+Compare to known references:
+- "This is about twice as complex as Feature X"
+- Use Fibonacci (1, 2, 3, 5, 8, 13) to reflect uncertainty
+
+### Task Decomposition
+1. Break into tasks <=4 hours
+2. If can't decompose, spike first
+3. Sum tasks + 20% integration buffer
+
+## Effort Multipliers
+
+| Factor | Multiplier |
+|--------|------------|
+| New technology | 1.5-2x |
+| Unclear requirements | 1.3-1.5x |
+| External dependencies (waiting on others) | 1.2-1.5x |
+| Legacy/undocumented code | 1.3-2x |
+| Production deployment | 1.2x |
+| First time doing X | 2-3x |
+| Context switching (other priorities) | 1.3x |
+| Yak shaving risk (unknown unknowns) | 1.5x |
+
+## Hidden Work Checklist
+
+Always include time for:
+- [ ] Code review (20% of dev time)
+- [ ] Testing (30-50% of dev time)
+- [ ] Documentation (10% of dev time)
+- [ ] Deployment/config (varies)
+- [ ] Bug fixes from testing (20% buffer)
+- [ ] Interruptions / competing priorities
+
+## When to Re-Estimate
+
+Re-estimate when:
+- Scope changes materially
+- Major unknown becomes known
+- Actual progress diverges >30% from estimate
+
+## Communicating Estimates
+
+**Good:** "1-2 weeks, confidence 70%-main risk is the third-party API integration"
+
+**Bad:** "About 2 weeks"
+
+Always include:
+1. Range, not point estimate
+2. Confidence level
+3. Key assumptions/risks