FA-97424 / Knitting and sewing pattern grading / Member archive

Yarn yardage estimator: safety margin · case 04

A 10% safety margin adds only 10 metres to a 2000 metre sweater.

Member previewVariant 4 · 3 implementations · 8 checks per implementation

Case contract

grams = garment_area / swatch_area * swatch_g; meters = grams * skein_m/skein_g; add margin_pct as a multiplier (meters*(1+margin/100)). skeins = ceiling(meters/skein_m); leftover = skeins*skein_m - meters. Return [meters, skeins, leftover] with meters and leftover half-up integers. Non-positive swatch area or skein weight -> "error: swatch".

Why this case matters

Designers and knitters estimate how many skeins to buy from a weighed swatch.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
with margin	`[1210, 10, 40]`	`[1320, 11, 55]`	Failed

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