FA-79356 / Barcode symbology encoding / Open access

EAN-13 centre guard starts with a bar · case 01

Scanners reject every symbol because the centre guard pattern is inverted.

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

ROOT CAUSE

The centre guard is written as 10101 instead of 01010.

VERIFIED REPAIR

The centre guard is space-bar-space-bar-space: 01010.

Unsuccessful approach: A four-module guard shifts the right half by one module.

Case contract

Encode a 13-character string of ASCII digits (the check digit is taken as given, not verified) as the 95-module EAN-13 pattern: start guard 101, six left digits in L or G sets chosen by the parity row of the leading digit, centre guard 01010, six right digits in the R set, end guard 101. R is the bitwise complement of L and G is R reversed. Anything else returns None.

Why this case matters

Retail, logistics, pharmacy and document workflows depend on encoders that produce exactly the module pattern, code-set switches, separators and quiet zones scanners expect; one misplaced module or separator makes a label unreadable or, worse, scan as different data.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(code):
    if len(code) != 13 or not all(ch in '0123456789' for ch in code):
        return None
    L = ['0001101', '0011001', '0010011', '0111101', '0100011', '0110001', '0101111', '0111011', '0110111', '0001011']
    R = [''.join('1' if b == '0' else '0' for b in p) for p in L]
    G = [p[::-1] for p in R]
    parity = ['LLLLLL', 'LLGLGG', 'LLGGLG', 'LLGGGL', 'LGLLGG', 'LGGLLG', 'LGGGLL', 'LGLGLG', 'LGLGGL', 'LGGLGL']
    pat = parity[int(code[0])]
    left = ''.join((L if pat[i] == 'L' else G)[int(code[1 + i])] for i in range(6))
    right = ''.join(R[int(ch)] for ch in code[7:])
    return '101' + left + '10101' + right + '101'
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['5569719879594', '10101100010000101001011101110110011001001011101010100100010001001110100100111011101001011100101'], ['3339552094472', '10101111010111101001011101110010111001001001101010111001011101001011100101110010001001101100101'], ['400638133393１', None], ['12345678901٣2', None], ['123456789012', None], ['12345678901234', None], ['', None], ['5564657964331', '10101100010000101001110101011110110001001000101010111010010100001011100100001010000101100110101']], [['0777861705172', '10101110110111011011101101101110101111001100101010100010011100101001110110011010001001101100101'], ['4641860725337', '10101011110011101001100101101110000101010011101010100010011011001001110100001010000101000100101'], ['12345678901٣2', None], ['123456789012', None], ['12345678901234', None], ['', None], ['400638133393１', None], ['6141838617595', '10100110010011101011001100010010111101011011101010101000011001101000100100111011101001001110101']], [['3716511088176', '10101110110011001000010101110010110011001100101010111001010010001001000110011010001001010000101'], ['7062168881750', '10100011010000101001001101100110101111000100101010100100010010001100110100010010011101110010101'], ['123456789012', None], ['12345678901234', None], ['', None], ['400638133393１', None], ['12345678901٣2', None], ['6191360813603', '10100110010010111011001101000010101111000110101010100100011001101000010101000011100101000010101']], [['1986892142891', '10100010110110111000010101101110010111001101101010110011010111001101100100100011101001100110101'], ['6274612745694', '10100100110010001001110100001010011001001001101010100010010111001001110101000011101001011100101'], ['12345678901234', None], ['', None], ['400638133393１', None], ['12345678901٣2', None], ['123456789012', None], ['6346382380419', '10101111010011101000010101000010110111001001101010100001010010001110010101110011001101110100101']], [['8746102916553', '10101110110011101010111101100110100111001001101010111010011001101010000100111010011101000010101'], ['4502760148617', '10101100010100111001001101110110000101010011101010110011010111001001000101000011001101000100101'], ['', None], ['400638133393１', None], ['12345678901٣2', None], ['123456789012', None], ['12345678901234', None], ['3842111701831', '10101101110100011001101101100110110011001100101010100010011100101100110100100010000101100110101']]]
labels = ["regression: centre guard pattern", "repair trap", "combined fault", "control", "control", "boundary", "boundary", "control"]
for i, (args, expected) in enumerate(fixtures[N-1]):
    check("%s %d" % (labels[i % len(labels)], i), 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
regression: centre guard pattern 0	`10101100010000101001011101110110011001001011110101100100010001001110100100111011101001011100101`	`10101100010000101001011101110110011001001011101010100100010001001110100100111011101001011100101`	Failed
repair trap 1	`10101111010111101001011101110010111001001001110101111001011101001011100101110010001001101100101`	`10101111010111101001011101110010111001001001101010111001011101001011100101110010001001101100101`	Failed
combined fault 2	`None`	`None`	Passed
control 3	`None`	`None`	Passed
control 4	`None`	`None`	Passed
boundary 5	`None`	`None`	Passed
boundary 6	`None`	`None`	Passed
control 7	`10101100010000101001110101011110110001001000110101111010010100001011100100001010000101100110101`	`10101100010000101001110101011110110001001000101010111010010100001011100100001010000101100110101`	Failed

SHA-256 / faea22c0c2b8f9046285e6cd7eb53003fcfbc84b41c41f1a64dd1c22cb7d58dc

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(code):
    if len(code) != 13 or not all(ch in '0123456789' for ch in code):
        return None
    L = ['0001101', '0011001', '0010011', '0111101', '0100011', '0110001', '0101111', '0111011', '0110111', '0001011']
    R = [''.join('1' if b == '0' else '0' for b in p) for p in L]
    G = [p[::-1] for p in R]
    parity = ['LLLLLL', 'LLGLGG', 'LLGGLG', 'LLGGGL', 'LGLLGG', 'LGGLLG', 'LGGGLL', 'LGLGLG', 'LGLGGL', 'LGGLGL']
    pat = parity[int(code[0])]
    left = ''.join((L if pat[i] == 'L' else G)[int(code[1 + i])] for i in range(6))
    right = ''.join(R[int(ch)] for ch in code[7:])
    return '101' + left + '0101' + right + '101'
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['5569719879594', '10101100010000101001011101110110011001001011101010100100010001001110100100111011101001011100101'], ['3339552094472', '10101111010111101001011101110010111001001001101010111001011101001011100101110010001001101100101'], ['400638133393１', None], ['12345678901٣2', None], ['123456789012', None], ['12345678901234', None], ['', None], ['5564657964331', '10101100010000101001110101011110110001001000101010111010010100001011100100001010000101100110101']], [['0777861705172', '10101110110111011011101101101110101111001100101010100010011100101001110110011010001001101100101'], ['4641860725337', '10101011110011101001100101101110000101010011101010100010011011001001110100001010000101000100101'], ['12345678901٣2', None], ['123456789012', None], ['12345678901234', None], ['', None], ['400638133393１', None], ['6141838617595', '10100110010011101011001100010010111101011011101010101000011001101000100100111011101001001110101']], [['3716511088176', '10101110110011001000010101110010110011001100101010111001010010001001000110011010001001010000101'], ['7062168881750', '10100011010000101001001101100110101111000100101010100100010010001100110100010010011101110010101'], ['123456789012', None], ['12345678901234', None], ['', None], ['400638133393１', None], ['12345678901٣2', None], ['6191360813603', '10100110010010111011001101000010101111000110101010100100011001101000010101000011100101000010101']], [['1986892142891', '10100010110110111000010101101110010111001101101010110011010111001101100100100011101001100110101'], ['6274612745694', '10100100110010001001110100001010011001001001101010100010010111001001110101000011101001011100101'], ['12345678901234', None], ['', None], ['400638133393１', None], ['12345678901٣2', None], ['123456789012', None], ['6346382380419', '10101111010011101000010101000010110111001001101010100001010010001110010101110011001101110100101']], [['8746102916553', '10101110110011101010111101100110100111001001101010111010011001101010000100111010011101000010101'], ['4502760148617', '10101100010100111001001101110110000101010011101010110011010111001001000101000011001101000100101'], ['', None], ['400638133393１', None], ['12345678901٣2', None], ['123456789012', None], ['12345678901234', None], ['3842111701831', '10101101110100011001101101100110110011001100101010100010011100101100110100100010000101100110101']]]
labels = ["regression: centre guard pattern", "repair trap", "combined fault", "control", "control", "boundary", "boundary", "control"]
for i, (args, expected) in enumerate(fixtures[N-1]):
    check("%s %d" % (labels[i % len(labels)], i), 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
regression: centre guard pattern 0	`1010110001000010100101110111011001100100101110101100100010001001110100100111011101001011100101`	`10101100010000101001011101110110011001001011101010100100010001001110100100111011101001011100101`	Failed
repair trap 1	`1010111101011110100101110111001011100100100110101111001011101001011100101110010001001101100101`	`10101111010111101001011101110010111001001001101010111001011101001011100101110010001001101100101`	Failed
combined fault 2	`None`	`None`	Passed
control 3	`None`	`None`	Passed
control 4	`None`	`None`	Passed
boundary 5	`None`	`None`	Passed
boundary 6	`None`	`None`	Passed
control 7	`1010110001000010100111010101111011000100100010101111010010100001011100100001010000101100110101`	`10101100010000101001110101011110110001001000101010111010010100001011100100001010000101100110101`	Failed

SHA-256 / ba35246a46d297a8de4c1bed9ef8d33d3f4ee49d1a0c0871e7449c68d946f090

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(code):
    if len(code) != 13 or not all(ch in '0123456789' for ch in code):
        return None
    L = ['0001101', '0011001', '0010011', '0111101', '0100011', '0110001', '0101111', '0111011', '0110111', '0001011']
    R = [''.join('1' if b == '0' else '0' for b in p) for p in L]
    G = [p[::-1] for p in R]
    parity = ['LLLLLL', 'LLGLGG', 'LLGGLG', 'LLGGGL', 'LGLLGG', 'LGGLLG', 'LGGGLL', 'LGLGLG', 'LGLGGL', 'LGGLGL']
    pat = parity[int(code[0])]
    left = ''.join((L if pat[i] == 'L' else G)[int(code[1 + i])] for i in range(6))
    right = ''.join(R[int(ch)] for ch in code[7:])
    return '101' + left + '01010' + right + '101'
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['5569719879594', '10101100010000101001011101110110011001001011101010100100010001001110100100111011101001011100101'], ['3339552094472', '10101111010111101001011101110010111001001001101010111001011101001011100101110010001001101100101'], ['400638133393１', None], ['12345678901٣2', None], ['123456789012', None], ['12345678901234', None], ['', None], ['5564657964331', '10101100010000101001110101011110110001001000101010111010010100001011100100001010000101100110101']], [['0777861705172', '10101110110111011011101101101110101111001100101010100010011100101001110110011010001001101100101'], ['4641860725337', '10101011110011101001100101101110000101010011101010100010011011001001110100001010000101000100101'], ['12345678901٣2', None], ['123456789012', None], ['12345678901234', None], ['', None], ['400638133393１', None], ['6141838617595', '10100110010011101011001100010010111101011011101010101000011001101000100100111011101001001110101']], [['3716511088176', '10101110110011001000010101110010110011001100101010111001010010001001000110011010001001010000101'], ['7062168881750', '10100011010000101001001101100110101111000100101010100100010010001100110100010010011101110010101'], ['123456789012', None], ['12345678901234', None], ['', None], ['400638133393１', None], ['12345678901٣2', None], ['6191360813603', '10100110010010111011001101000010101111000110101010100100011001101000010101000011100101000010101']], [['1986892142891', '10100010110110111000010101101110010111001101101010110011010111001101100100100011101001100110101'], ['6274612745694', '10100100110010001001110100001010011001001001101010100010010111001001110101000011101001011100101'], ['12345678901234', None], ['', None], ['400638133393１', None], ['12345678901٣2', None], ['123456789012', None], ['6346382380419', '10101111010011101000010101000010110111001001101010100001010010001110010101110011001101110100101']], [['8746102916553', '10101110110011101010111101100110100111001001101010111010011001101010000100111010011101000010101'], ['4502760148617', '10101100010100111001001101110110000101010011101010110011010111001001000101000011001101000100101'], ['', None], ['400638133393１', None], ['12345678901٣2', None], ['123456789012', None], ['12345678901234', None], ['3842111701831', '10101101110100011001101101100110110011001100101010100010011100101100110100100010000101100110101']]]
labels = ["regression: centre guard pattern", "repair trap", "combined fault", "control", "control", "boundary", "boundary", "control"]
for i, (args, expected) in enumerate(fixtures[N-1]):
    check("%s %d" % (labels[i % len(labels)], i), 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
regression: centre guard pattern 0	`10101100010000101001011101110110011001001011101010100100010001001110100100111011101001011100101`	`10101100010000101001011101110110011001001011101010100100010001001110100100111011101001011100101`	Passed
repair trap 1	`10101111010111101001011101110010111001001001101010111001011101001011100101110010001001101100101`	`10101111010111101001011101110010111001001001101010111001011101001011100101110010001001101100101`	Passed
combined fault 2	`None`	`None`	Passed
control 3	`None`	`None`	Passed
control 4	`None`	`None`	Passed
boundary 5	`None`	`None`	Passed
boundary 6	`None`	`None`	Passed
control 7	`10101100010000101001110101011110110001001000101010111010010100001011100100001010000101100110101`	`10101100010000101001110101011110110001001000101010111010010100001011100100001010000101100110101`	Passed

SHA-256 / dc93b3cc112392e239637ab260971871f8f3bd7bbadf39a9b3353a54f996cefa

Verification & scope

A deterministic bounded teaching model with a stipulated contract; it makes no claim of conformance to any published specification. 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 2026-09-29T14:49:43.801711+00:00.

Case digest / 193228eee656c9b0633a1133457c727aab79db0b7b1dbf0dafd49c34e2ab8b1a