## Severity: Low (backlog) HyperFormula's `ErrorType` enum does not include `CALC`. Excel uses `#CALC!` for several conditions: - Zero dimensions in array functions (`=SEQUENCE(0)`, `=SEQUENCE(1,0)`) - Empty array results - Certain spill-related errors (separate from `#SPILL!`) Currently these are mapped to `ErrorType.NUM` (`#NUM!`), which is the closest semantic match but diverges from Excel. ## Known affected locations - `SequencePlugin.ts` — zero dimension check returns `#NUM!` instead of `#CALC!` - Potentially other array functions ## Scope Adding `ErrorType.CALC` would require: - New enum value in `src/Cell.ts` - New error message in `src/error-message.ts` - Export handling in `CellValueExporter` - Updates to functions currently returning `#NUM!` where `#CALC!` is correct - Test updates ## Impact Cosmetic divergence from Excel. Does not affect functionality — formulas still error correctly, just with a different error type. Low priority unless Excel compatibility audit (2026 roadmap) prioritizes exact error type matching. Found during SEQUENCE implementation (PR #1645).