FA-97516 / Knitting and sewing pattern grading / Open access

Sewing pattern grade rule stepper: step interval size · case 01

Grading from 14 to 16 uses the large increment though the step starts below the break.

Verified by executionVariant 1 · 8 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The increment is chosen from the destination size of each step instead of its lower size.

VERIFIED REPAIR

Use the lower size of the step interval.

Unsuccessful approach: Using the start size is right going up but wrong going down.

Case contract

Sizes 6..22 in steps of 2 (others -> "error: size"). Grading one size step between sizes s and s+2 changes the circumference by `small` cm if the lower size s < brk, else `large`. Going down subtracts the same step amounts. Return [circumference, per quarter-panel = circumference/4], both half-up to 0.1.

Why this case matters

Sewing pattern grading applies different increments above a size break and distributes them across front and back pieces.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import math
from fractions import Fraction
N = 1
observations = []
def solve(base_size, target_size, base_cm, small, large, brk):
    SIZES = [6, 8, 10, 12, 14, 16, 18, 20, 22]
    if base_size not in SIZES or target_size not in SIZES:
        return 'error: size'
    i, j = SIZES.index(base_size), SIZES.index(target_size)
    m = Fraction(str(base_cm))
    step = 1 if j > i else -1
    k = i
    while k != j:
        lo = k + step
        inc = small if SIZES[lo] < brk else large
        m += step * inc
        k += step
    q = m / 4
    return [math.floor(m * 10 + Fraction(1, 2)) / 10, math.floor(q * 10 + Fraction(1, 2)) / 10]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['same size', [12, 12, '92.5', 5, 6, 16], [92.5, 23.1]],
  ['across the break', [14, 20, '96', 5, 6, 16], [113.0, 28.3]],
  ['down across the break', [20, 14, '110', 5, 6, 16], [93.0, 23.3]],
  ['regression: step interval size', [10, 20, '92.5', 4, 6, 16], [116.5, 29.1]],
  ['repair check: step interval size', [20, 8, '92.5', 4, 7, 16], [62.5, 15.6]],
  ['generated control 1', [14, 16, '96', 4, 7, 12], [103.0, 25.8]],
  ['generated control 2', [18, 16, '100', 5, 7, 16], [93.0, 23.3]],
  ['generated control 3', [16, 16, '96', 5, 7, 14], [96.0, 24.0]]],
 [['across the break', [14, 20, '96', 5, 6, 16], [113.0, 28.3]],
  ['down across the break', [20, 14, '110', 5, 6, 16], [93.0, 23.3]],
  ['unknown size', [12, 24, '92', 5, 6, 16], 'error: size'],
  ['regression: step interval size', [6, 18, '92.5', 5, 7, 18], [122.5, 30.6]],
  ['repair check: step interval size', [14, 10, '92.5', 5, 6, 12], [81.5, 20.4]],
  ['generated control 1', [12, 14, '92.5', 5, 7, 18], [97.5, 24.4]],
  ['generated control 2', [18, 10, '96', 4, 7, 14], [74.0, 18.5]],
  ['generated control 3', [16, 14, '88', 4, 6, 14], [82.0, 20.5]]],
 [['down across the break', [20, 14, '110', 5, 6, 16], [93.0, 23.3]],
  ['unknown size', [12, 24, '92', 5, 6, 16], 'error: size'],
  ['same size', [12, 12, '92.5', 5, 6, 16], [92.5, 23.1]],
  ['regression: step interval size', [10, 22, '88', 4, 6, 12], [122.0, 30.5]],
  ['repair check: step interval size', [14, 10, '100', 4, 6, 14], [92.0, 23.0]],
  ['generated control 1', [6, 6, '88', 4, 7, 14], [88.0, 22.0]],
  ['generated control 2', [16, 22, '88', 4, 6, 14], [106.0, 26.5]],
  ['generated control 3', [20, 20, '88', 5, 6, 16], [88.0, 22.0]]],
 [['unknown size', [12, 24, '92', 5, 6, 16], 'error: size'],
  ['same size', [12, 12, '92.5', 5, 6, 16], [92.5, 23.1]],
  ['across the break', [14, 20, '96', 5, 6, 16], [113.0, 28.3]],
  ['regression: step interval size', [10, 22, '88', 5, 7, 12], [128.0, 32.0]],
  ['repair check: step interval size', [22, 14, '100', 5, 6, 16], [77.0, 19.3]],
  ['generated control 1', [8, 6, '88', 5, 7, 16], [83.0, 20.8]],
  ['generated control 2', [16, 20, '100', 5, 7, 14], [114.0, 28.5]],
  ['generated control 3', [12, 6, '92.5', 5, 7, 14], [77.5, 19.4]]],
 [['same size', [12, 12, '92.5', 5, 6, 16], [92.5, 23.1]],
  ['across the break', [14, 20, '96', 5, 6, 16], [113.0, 28.3]],
  ['down across the break', [20, 14, '110', 5, 6, 16], [93.0, 23.3]],
  ['regression: step interval size', [12, 20, '100', 4, 7, 18], [119.0, 29.8]],
  ['repair check: step interval size', [18, 16, '96', 4, 6, 18], [92.0, 23.0]],
  ['generated control 1', [10, 16, '100', 5, 6, 14], [116.0, 29.0]],
  ['generated control 2', [12, 18, '100', 4, 7, 14], [118.0, 29.5]],
  ['generated control 3', [16, 8, '96', 5, 7, 14], [74.0, 18.5]]]]
for label, args, expected in fixtures[N - 1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
same size	`[92.5, 23.1]`	`[92.5, 23.1]`	Passed
across the break	`[114.0, 28.5]`	`[113.0, 28.3]`	Failed
down across the break	`[93.0, 23.3]`	`[93.0, 23.3]`	Passed
regression: step interval size	`[118.5, 29.6]`	`[116.5, 29.1]`	Failed
repair check: step interval size	`[62.5, 15.6]`	`[62.5, 15.6]`	Passed
generated control 1	`[103.0, 25.8]`	`[103.0, 25.8]`	Passed
generated control 2	`[93.0, 23.3]`	`[93.0, 23.3]`	Passed
generated control 3	`[96.0, 24.0]`	`[96.0, 24.0]`	Passed

SHA-256 / 0897b252d25ee0814b62b5c7316570b6e12f87e4590d6a5a1a31d8c38d8c5f7d

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import math
from fractions import Fraction
N = 1
observations = []
def solve(base_size, target_size, base_cm, small, large, brk):
    SIZES = [6, 8, 10, 12, 14, 16, 18, 20, 22]
    if base_size not in SIZES or target_size not in SIZES:
        return 'error: size'
    i, j = SIZES.index(base_size), SIZES.index(target_size)
    m = Fraction(str(base_cm))
    step = 1 if j > i else -1
    k = i
    while k != j:
        lo = k
        inc = small if SIZES[lo] < brk else large
        m += step * inc
        k += step
    q = m / 4
    return [math.floor(m * 10 + Fraction(1, 2)) / 10, math.floor(q * 10 + Fraction(1, 2)) / 10]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['same size', [12, 12, '92.5', 5, 6, 16], [92.5, 23.1]],
  ['across the break', [14, 20, '96', 5, 6, 16], [113.0, 28.3]],
  ['down across the break', [20, 14, '110', 5, 6, 16], [93.0, 23.3]],
  ['regression: step interval size', [10, 20, '92.5', 4, 6, 16], [116.5, 29.1]],
  ['repair check: step interval size', [20, 8, '92.5', 4, 7, 16], [62.5, 15.6]],
  ['generated control 1', [14, 16, '96', 4, 7, 12], [103.0, 25.8]],
  ['generated control 2', [18, 16, '100', 5, 7, 16], [93.0, 23.3]],
  ['generated control 3', [16, 16, '96', 5, 7, 14], [96.0, 24.0]]],
 [['across the break', [14, 20, '96', 5, 6, 16], [113.0, 28.3]],
  ['down across the break', [20, 14, '110', 5, 6, 16], [93.0, 23.3]],
  ['unknown size', [12, 24, '92', 5, 6, 16], 'error: size'],
  ['regression: step interval size', [6, 18, '92.5', 5, 7, 18], [122.5, 30.6]],
  ['repair check: step interval size', [14, 10, '92.5', 5, 6, 12], [81.5, 20.4]],
  ['generated control 1', [12, 14, '92.5', 5, 7, 18], [97.5, 24.4]],
  ['generated control 2', [18, 10, '96', 4, 7, 14], [74.0, 18.5]],
  ['generated control 3', [16, 14, '88', 4, 6, 14], [82.0, 20.5]]],
 [['down across the break', [20, 14, '110', 5, 6, 16], [93.0, 23.3]],
  ['unknown size', [12, 24, '92', 5, 6, 16], 'error: size'],
  ['same size', [12, 12, '92.5', 5, 6, 16], [92.5, 23.1]],
  ['regression: step interval size', [10, 22, '88', 4, 6, 12], [122.0, 30.5]],
  ['repair check: step interval size', [14, 10, '100', 4, 6, 14], [92.0, 23.0]],
  ['generated control 1', [6, 6, '88', 4, 7, 14], [88.0, 22.0]],
  ['generated control 2', [16, 22, '88', 4, 6, 14], [106.0, 26.5]],
  ['generated control 3', [20, 20, '88', 5, 6, 16], [88.0, 22.0]]],
 [['unknown size', [12, 24, '92', 5, 6, 16], 'error: size'],
  ['same size', [12, 12, '92.5', 5, 6, 16], [92.5, 23.1]],
  ['across the break', [14, 20, '96', 5, 6, 16], [113.0, 28.3]],
  ['regression: step interval size', [10, 22, '88', 5, 7, 12], [128.0, 32.0]],
  ['repair check: step interval size', [22, 14, '100', 5, 6, 16], [77.0, 19.3]],
  ['generated control 1', [8, 6, '88', 5, 7, 16], [83.0, 20.8]],
  ['generated control 2', [16, 20, '100', 5, 7, 14], [114.0, 28.5]],
  ['generated control 3', [12, 6, '92.5', 5, 7, 14], [77.5, 19.4]]],
 [['same size', [12, 12, '92.5', 5, 6, 16], [92.5, 23.1]],
  ['across the break', [14, 20, '96', 5, 6, 16], [113.0, 28.3]],
  ['down across the break', [20, 14, '110', 5, 6, 16], [93.0, 23.3]],
  ['regression: step interval size', [12, 20, '100', 4, 7, 18], [119.0, 29.8]],
  ['repair check: step interval size', [18, 16, '96', 4, 6, 18], [92.0, 23.0]],
  ['generated control 1', [10, 16, '100', 5, 6, 14], [116.0, 29.0]],
  ['generated control 2', [12, 18, '100', 4, 7, 14], [118.0, 29.5]],
  ['generated control 3', [16, 8, '96', 5, 7, 14], [74.0, 18.5]]]]
for label, args, expected in fixtures[N - 1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
same size	`[92.5, 23.1]`	`[92.5, 23.1]`	Passed
across the break	`[113.0, 28.3]`	`[113.0, 28.3]`	Passed
down across the break	`[92.0, 23.0]`	`[93.0, 23.3]`	Failed
regression: step interval size	`[116.5, 29.1]`	`[116.5, 29.1]`	Passed
repair check: step interval size	`[59.5, 14.9]`	`[62.5, 15.6]`	Failed
generated control 1	`[103.0, 25.8]`	`[103.0, 25.8]`	Passed
generated control 2	`[93.0, 23.3]`	`[93.0, 23.3]`	Passed
generated control 3	`[96.0, 24.0]`	`[96.0, 24.0]`	Passed

SHA-256 / 40aaa3a81327074c2028d13d4c46b52d0b32931f141d9d8e416b5e5c6e5f063d

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json
import math
from fractions import Fraction
N = 1
observations = []
def solve(base_size, target_size, base_cm, small, large, brk):
    SIZES = [6, 8, 10, 12, 14, 16, 18, 20, 22]
    if base_size not in SIZES or target_size not in SIZES:
        return 'error: size'
    i, j = SIZES.index(base_size), SIZES.index(target_size)
    m = Fraction(str(base_cm))
    step = 1 if j > i else -1
    k = i
    while k != j:
        lo = min(k, k + step)
        inc = small if SIZES[lo] < brk else large
        m += step * inc
        k += step
    q = m / 4
    return [math.floor(m * 10 + Fraction(1, 2)) / 10, math.floor(q * 10 + Fraction(1, 2)) / 10]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['same size', [12, 12, '92.5', 5, 6, 16], [92.5, 23.1]],
  ['across the break', [14, 20, '96', 5, 6, 16], [113.0, 28.3]],
  ['down across the break', [20, 14, '110', 5, 6, 16], [93.0, 23.3]],
  ['regression: step interval size', [10, 20, '92.5', 4, 6, 16], [116.5, 29.1]],
  ['repair check: step interval size', [20, 8, '92.5', 4, 7, 16], [62.5, 15.6]],
  ['generated control 1', [14, 16, '96', 4, 7, 12], [103.0, 25.8]],
  ['generated control 2', [18, 16, '100', 5, 7, 16], [93.0, 23.3]],
  ['generated control 3', [16, 16, '96', 5, 7, 14], [96.0, 24.0]]],
 [['across the break', [14, 20, '96', 5, 6, 16], [113.0, 28.3]],
  ['down across the break', [20, 14, '110', 5, 6, 16], [93.0, 23.3]],
  ['unknown size', [12, 24, '92', 5, 6, 16], 'error: size'],
  ['regression: step interval size', [6, 18, '92.5', 5, 7, 18], [122.5, 30.6]],
  ['repair check: step interval size', [14, 10, '92.5', 5, 6, 12], [81.5, 20.4]],
  ['generated control 1', [12, 14, '92.5', 5, 7, 18], [97.5, 24.4]],
  ['generated control 2', [18, 10, '96', 4, 7, 14], [74.0, 18.5]],
  ['generated control 3', [16, 14, '88', 4, 6, 14], [82.0, 20.5]]],
 [['down across the break', [20, 14, '110', 5, 6, 16], [93.0, 23.3]],
  ['unknown size', [12, 24, '92', 5, 6, 16], 'error: size'],
  ['same size', [12, 12, '92.5', 5, 6, 16], [92.5, 23.1]],
  ['regression: step interval size', [10, 22, '88', 4, 6, 12], [122.0, 30.5]],
  ['repair check: step interval size', [14, 10, '100', 4, 6, 14], [92.0, 23.0]],
  ['generated control 1', [6, 6, '88', 4, 7, 14], [88.0, 22.0]],
  ['generated control 2', [16, 22, '88', 4, 6, 14], [106.0, 26.5]],
  ['generated control 3', [20, 20, '88', 5, 6, 16], [88.0, 22.0]]],
 [['unknown size', [12, 24, '92', 5, 6, 16], 'error: size'],
  ['same size', [12, 12, '92.5', 5, 6, 16], [92.5, 23.1]],
  ['across the break', [14, 20, '96', 5, 6, 16], [113.0, 28.3]],
  ['regression: step interval size', [10, 22, '88', 5, 7, 12], [128.0, 32.0]],
  ['repair check: step interval size', [22, 14, '100', 5, 6, 16], [77.0, 19.3]],
  ['generated control 1', [8, 6, '88', 5, 7, 16], [83.0, 20.8]],
  ['generated control 2', [16, 20, '100', 5, 7, 14], [114.0, 28.5]],
  ['generated control 3', [12, 6, '92.5', 5, 7, 14], [77.5, 19.4]]],
 [['same size', [12, 12, '92.5', 5, 6, 16], [92.5, 23.1]],
  ['across the break', [14, 20, '96', 5, 6, 16], [113.0, 28.3]],
  ['down across the break', [20, 14, '110', 5, 6, 16], [93.0, 23.3]],
  ['regression: step interval size', [12, 20, '100', 4, 7, 18], [119.0, 29.8]],
  ['repair check: step interval size', [18, 16, '96', 4, 6, 18], [92.0, 23.0]],
  ['generated control 1', [10, 16, '100', 5, 6, 14], [116.0, 29.0]],
  ['generated control 2', [12, 18, '100', 4, 7, 14], [118.0, 29.5]],
  ['generated control 3', [16, 8, '96', 5, 7, 14], [74.0, 18.5]]]]
for label, args, expected in fixtures[N - 1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
same size	`[92.5, 23.1]`	`[92.5, 23.1]`	Passed
across the break	`[113.0, 28.3]`	`[113.0, 28.3]`	Passed
down across the break	`[93.0, 23.3]`	`[93.0, 23.3]`	Passed
regression: step interval size	`[116.5, 29.1]`	`[116.5, 29.1]`	Passed
repair check: step interval size	`[62.5, 15.6]`	`[62.5, 15.6]`	Passed
generated control 1	`[103.0, 25.8]`	`[103.0, 25.8]`	Passed
generated control 2	`[93.0, 23.3]`	`[93.0, 23.3]`	Passed
generated control 3	`[96.0, 24.0]`	`[96.0, 24.0]`	Passed

SHA-256 / 25c4e95d1e1e2838dde710895370ab706a3f79297f8462a234b7cf52f9c92d91

Verification & scope

A deterministic toy contract stated in full here; it is a bounded teaching model, not an authoritative reference or standards implementation. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:52:33.008192+00:00.

Case digest / 6503435ff3fd7767b2d463978ed4b4ce3b92bfaf0f2700ddc32e370acb616cc3