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Marc-André BombeckandClaude Opus 4.7
af77e5ecf8
Marc reported clicking "All" on a chart's range buttons displayed "+0.0 kg/Woche" even when his weight clearly drifted across years. Root cause: `weeklyDelta = (lastTrend - firstTrend) / windowDays * 7` is mathematically correct but the per-week rate becomes vanishingly small for multi-year windows (~0.07 kg/week for 10 kg over 3 years), and the 1-decimal `fmt.number(delta, 1)` formatter rounds it to "0.0". Fix: extract a pure `computeWindowTrend()` helper at `src/lib/analytics/window-trend.ts`. For windows ≥ 90 days we additionally surface a split-half delta — the mean of the second half of the visible series minus the mean of the first half. That number cannot round to zero unless the metric truly didn't move, and it's exactly what Marc wants to see when he asks "what changed across all my data?". For short windows the per-week rate stays the only display because it's still the most actionable metric there. The chart trend line surfaces both: "WEIGHT: +0.1 kg/week (0.1 %/week) · Total +5.4 kg (6.7 %)" on the All view of a multi-year account. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>