[Feature] Custom calculated ratios — user-defined marker formulas #62
Description
Description
Allow users to define custom calculated markers with formulas like Marker A / Marker B. The result auto-computes whenever both source values exist for a date.
Currently, the three built-in calculated markers (BUN/Creatinine Ratio, Free Water Deficit, PhenoAge) are hardcoded. This would let users create their own without code changes.
Scope
- Formula UI: pick two markers + operator (÷, ×, −, +) — or eventually free-form expressions
- Dependency tracking: recalculate when source values change or are imported
- Edge cases: missing values → null, division by zero → null, unit inference
- Integration with import, export, manual entry (read-only values, editable formula)
Notes
This is a natural extension of the existing custom marker system. Lower priority — users can work around it by manually entering ratio values into the Calculated Ratios category.