FAILURE MAP
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FA-69216 / Tide and marine navigation tables / Open access

Light geographic and visible range: Heights are added under a single square root · case 01

Lights are raised far too late.

Verified by executionVariant 1 · 7 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The geographic range is computed from sqrt(he+hl) instead of adding the two horizon distances.

THE FAILURE

The geographic range is computed from sqrt(he+hl) instead of adding the two horizon distances.

Unsuccessful approach: Applying the 2.08 factor only to the observer term understates the light horizon.

Case contract

Input [he, hl, nominal, mhws, tide]: observer height of eye (m), light elevation charted above MHWS (m), nominal range (nm), MHWS and current tide above datum. Effective light height = hl+(mhws-tide). Geographic range = 2.08*(sqrt(he)+sqrt(effective)). Visible range = min(geographic, nominal); the limit is "geographic" when geographic<nominal else "luminous". Return [geo rounded 1, visible rounded 1, limit].

Why this case matters

Tide tables and passage plans turn published predictions into go/no-go decisions about depth, clearance and timing.

1 / The failure

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(x):
    he,hl,nom,mhws,tide=x
    hle=hl+(mhws-tide)
    geo=2.08*math.sqrt(he+hle)
    vis=min(geo,nom)
    lim='geographic' if geo<nom else 'luminous'
    return [round(geo,1),round(vis,1),lim]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('light geographic and visible range [3, 25, 18, 4.5, 1.0]', [3, 25, 18, 4.5, 1.0], [14.7, 14.7, 'geographic']), ('light geographic and visible range [3, 25, 10, 4.5, 1.0]', [3, 25, 10, 4.5, 1.0], [14.7, 10, 'luminous']), ('light geographic and visible range [9, 64, 23, 5.0, 5.0]', [9, 64, 23, 5.0, 5.0], [22.9, 22.9, 'geographic']), ('light geographic and visible range [1.5, 12, 20, 4.0, 0.5]', [1.5, 12, 20, 4.0, 0.5], [10.7, 10.7, 'geographic']), ('light geographic and visible range [16, 36, 20.8, 3.0, 3.0]', [16, 36, 20.8, 3.0, 3.0], [20.8, 20.8, 'luminous']), ('light geographic and visible range [4, 9, 10.4, 2.0, 2.0]', [4, 9, 10.4, 2.0, 2.0], [10.4, 10.4, 'luminous']), ('light geographic and visible range [2, 40, 15, 4.0, 6.0]', [2, 40, 15, 4.0, 6.0], [15.8, 15, 'luminous'])], [('light geographic and visible range [3, 25, 10, 4.5, 1.0]', [3, 25, 10, 4.5, 1.0], [14.7, 10, 'luminous']), ('light geographic and visible range [1.5, 12, 20, 4.0, 0.5]', [1.5, 12, 20, 4.0, 0.5], [10.7, 10.7, 'geographic']), ('light geographic and visible range [16, 36, 20.8, 3.0, 3.0]', [16, 36, 20.8, 3.0, 3.0], [20.8, 20.8, 'luminous']), ('light geographic and visible range [4, 9, 10.4, 2.0, 2.0]', [4, 9, 10.4, 2.0, 2.0], [10.4, 10.4, 'luminous']), ('light geographic and visible range [2, 40, 15, 4.0, 6.0]', [2, 40, 15, 4.0, 6.0], [15.8, 15, 'luminous']), ('light geographic and visible range [12, 80, 30, 5.0, 2.0]', [12, 80, 30, 5.0, 2.0], [26.2, 26.2, 'geographic']), ('light geographic and visible range [5, 5, 6, 3.0, 1.0]', [5, 5, 6, 3.0, 1.0], [10.2, 6, 'luminous'])], [('light geographic and visible range [9, 64, 23, 5.0, 5.0]', [9, 64, 23, 5.0, 5.0], [22.9, 22.9, 'geographic']), ('light geographic and visible range [2, 40, 15, 4.0, 6.0]', [2, 40, 15, 4.0, 6.0], [15.8, 15, 'luminous']), ('light geographic and visible range [12, 80, 30, 5.0, 2.0]', [12, 80, 30, 5.0, 2.0], [26.2, 26.2, 'geographic']), ('light geographic and visible range [5, 5, 6, 3.0, 1.0]', [5, 5, 6, 3.0, 1.0], [10.2, 6, 'luminous']), ('light geographic and visible range [25, 100, 28, 4.0, 4.0]', [25, 100, 28, 4.0, 4.0], [31.2, 28, 'luminous']), ('light geographic and visible range [4, 16, 12.48, 3.0, 3.0]', [4, 16, 12.48, 3.0, 3.0], [12.5, 12.5, 'luminous']), ('light geographic and visible range [4, 9.174, 10.48, 2.0, 2.0]', [4, 9.174, 10.48, 2.0, 2.0], [10.5, 10.5, 'geographic'])], [('light geographic and visible range [1.5, 12, 20, 4.0, 0.5]', [1.5, 12, 20, 4.0, 0.5], [10.7, 10.7, 'geographic']), ('light geographic and visible range [25, 100, 28, 4.0, 4.0]', [25, 100, 28, 4.0, 4.0], [31.2, 28, 'luminous']), ('light geographic and visible range [4, 16, 12.48, 3.0, 3.0]', [4, 16, 12.48, 3.0, 3.0], [12.5, 12.5, 'luminous']), ('light geographic and visible range [4, 9.174, 10.48, 2.0, 2.0]', [4, 9.174, 10.48, 2.0, 2.0], [10.5, 10.5, 'geographic']), ('light geographic and visible range [3, 25, 18, 4.5, 1.0]', [3, 25, 18, 4.5, 1.0], [14.7, 14.7, 'geographic']), ('light geographic and visible range [3, 25, 10, 4.5, 1.0]', [3, 25, 10, 4.5, 1.0], [14.7, 10, 'luminous']), ('light geographic and visible range [9, 64, 23, 5.0, 5.0]', [9, 64, 23, 5.0, 5.0], [22.9, 22.9, 'geographic'])], [('light geographic and visible range [16, 36, 20.8, 3.0, 3.0]', [16, 36, 20.8, 3.0, 3.0], [20.8, 20.8, 'luminous']), ('light geographic and visible range [3, 25, 18, 4.5, 1.0]', [3, 25, 18, 4.5, 1.0], [14.7, 14.7, 'geographic']), ('light geographic and visible range [3, 25, 10, 4.5, 1.0]', [3, 25, 10, 4.5, 1.0], [14.7, 10, 'luminous']), ('light geographic and visible range [9, 64, 23, 5.0, 5.0]', [9, 64, 23, 5.0, 5.0], [22.9, 22.9, 'geographic']), ('light geographic and visible range [1.5, 12, 20, 4.0, 0.5]', [1.5, 12, 20, 4.0, 0.5], [10.7, 10.7, 'geographic']), ('light geographic and visible range [4, 9, 10.4, 2.0, 2.0]', [4, 9, 10.4, 2.0, 2.0], [10.4, 10.4, 'luminous']), ('light geographic and visible range [2, 40, 15, 4.0, 6.0]', [2, 40, 15, 4.0, 6.0], [15.8, 15, 'luminous'])]]
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 fixtureActualExpectedOutcome
light geographic and visible range [3, 25, 18, 4.5, 1.0][11.7, 11.7, 'geographic'][14.7, 14.7, 'geographic']Failed
light geographic and visible range [3, 25, 10, 4.5, 1.0][11.7, 10, 'luminous'][14.7, 10, 'luminous']Failed
light geographic and visible range [9, 64, 23, 5.0, 5.0][17.8, 17.8, 'geographic'][22.9, 22.9, 'geographic']Failed
light geographic and visible range [1.5, 12, 20, 4.0, 0.5][8.6, 8.6, 'geographic'][10.7, 10.7, 'geographic']Failed
light geographic and visible range [16, 36, 20.8, 3.0, 3.0][15.0, 15.0, 'geographic'][20.8, 20.8, 'luminous']Failed
light geographic and visible range [4, 9, 10.4, 2.0, 2.0][7.5, 7.5, 'geographic'][10.4, 10.4, 'luminous']Failed
light geographic and visible range [2, 40, 15, 4.0, 6.0][13.2, 13.2, 'geographic'][15.8, 15, 'luminous']Failed

SHA-256 / 67ab8bd81ca28f9972edbc3b139fe2958df383191827e9eae5258739efb8c0d6

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(x):
    he,hl,nom,mhws,tide=x
    hle=hl+(mhws-tide)
    geo=2.08*math.sqrt(he)+math.sqrt(hle)
    vis=min(geo,nom)
    lim='geographic' if geo<nom else 'luminous'
    return [round(geo,1),round(vis,1),lim]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('light geographic and visible range [3, 25, 18, 4.5, 1.0]', [3, 25, 18, 4.5, 1.0], [14.7, 14.7, 'geographic']), ('light geographic and visible range [3, 25, 10, 4.5, 1.0]', [3, 25, 10, 4.5, 1.0], [14.7, 10, 'luminous']), ('light geographic and visible range [9, 64, 23, 5.0, 5.0]', [9, 64, 23, 5.0, 5.0], [22.9, 22.9, 'geographic']), ('light geographic and visible range [1.5, 12, 20, 4.0, 0.5]', [1.5, 12, 20, 4.0, 0.5], [10.7, 10.7, 'geographic']), ('light geographic and visible range [16, 36, 20.8, 3.0, 3.0]', [16, 36, 20.8, 3.0, 3.0], [20.8, 20.8, 'luminous']), ('light geographic and visible range [4, 9, 10.4, 2.0, 2.0]', [4, 9, 10.4, 2.0, 2.0], [10.4, 10.4, 'luminous']), ('light geographic and visible range [2, 40, 15, 4.0, 6.0]', [2, 40, 15, 4.0, 6.0], [15.8, 15, 'luminous'])], [('light geographic and visible range [3, 25, 10, 4.5, 1.0]', [3, 25, 10, 4.5, 1.0], [14.7, 10, 'luminous']), ('light geographic and visible range [1.5, 12, 20, 4.0, 0.5]', [1.5, 12, 20, 4.0, 0.5], [10.7, 10.7, 'geographic']), ('light geographic and visible range [16, 36, 20.8, 3.0, 3.0]', [16, 36, 20.8, 3.0, 3.0], [20.8, 20.8, 'luminous']), ('light geographic and visible range [4, 9, 10.4, 2.0, 2.0]', [4, 9, 10.4, 2.0, 2.0], [10.4, 10.4, 'luminous']), ('light geographic and visible range [2, 40, 15, 4.0, 6.0]', [2, 40, 15, 4.0, 6.0], [15.8, 15, 'luminous']), ('light geographic and visible range [12, 80, 30, 5.0, 2.0]', [12, 80, 30, 5.0, 2.0], [26.2, 26.2, 'geographic']), ('light geographic and visible range [5, 5, 6, 3.0, 1.0]', [5, 5, 6, 3.0, 1.0], [10.2, 6, 'luminous'])], [('light geographic and visible range [9, 64, 23, 5.0, 5.0]', [9, 64, 23, 5.0, 5.0], [22.9, 22.9, 'geographic']), ('light geographic and visible range [2, 40, 15, 4.0, 6.0]', [2, 40, 15, 4.0, 6.0], [15.8, 15, 'luminous']), ('light geographic and visible range [12, 80, 30, 5.0, 2.0]', [12, 80, 30, 5.0, 2.0], [26.2, 26.2, 'geographic']), ('light geographic and visible range [5, 5, 6, 3.0, 1.0]', [5, 5, 6, 3.0, 1.0], [10.2, 6, 'luminous']), ('light geographic and visible range [25, 100, 28, 4.0, 4.0]', [25, 100, 28, 4.0, 4.0], [31.2, 28, 'luminous']), ('light geographic and visible range [4, 16, 12.48, 3.0, 3.0]', [4, 16, 12.48, 3.0, 3.0], [12.5, 12.5, 'luminous']), ('light geographic and visible range [4, 9.174, 10.48, 2.0, 2.0]', [4, 9.174, 10.48, 2.0, 2.0], [10.5, 10.5, 'geographic'])], [('light geographic and visible range [1.5, 12, 20, 4.0, 0.5]', [1.5, 12, 20, 4.0, 0.5], [10.7, 10.7, 'geographic']), ('light geographic and visible range [25, 100, 28, 4.0, 4.0]', [25, 100, 28, 4.0, 4.0], [31.2, 28, 'luminous']), ('light geographic and visible range [4, 16, 12.48, 3.0, 3.0]', [4, 16, 12.48, 3.0, 3.0], [12.5, 12.5, 'luminous']), ('light geographic and visible range [4, 9.174, 10.48, 2.0, 2.0]', [4, 9.174, 10.48, 2.0, 2.0], [10.5, 10.5, 'geographic']), ('light geographic and visible range [3, 25, 18, 4.5, 1.0]', [3, 25, 18, 4.5, 1.0], [14.7, 14.7, 'geographic']), ('light geographic and visible range [3, 25, 10, 4.5, 1.0]', [3, 25, 10, 4.5, 1.0], [14.7, 10, 'luminous']), ('light geographic and visible range [9, 64, 23, 5.0, 5.0]', [9, 64, 23, 5.0, 5.0], [22.9, 22.9, 'geographic'])], [('light geographic and visible range [16, 36, 20.8, 3.0, 3.0]', [16, 36, 20.8, 3.0, 3.0], [20.8, 20.8, 'luminous']), ('light geographic and visible range [3, 25, 18, 4.5, 1.0]', [3, 25, 18, 4.5, 1.0], [14.7, 14.7, 'geographic']), ('light geographic and visible range [3, 25, 10, 4.5, 1.0]', [3, 25, 10, 4.5, 1.0], [14.7, 10, 'luminous']), ('light geographic and visible range [9, 64, 23, 5.0, 5.0]', [9, 64, 23, 5.0, 5.0], [22.9, 22.9, 'geographic']), ('light geographic and visible range [1.5, 12, 20, 4.0, 0.5]', [1.5, 12, 20, 4.0, 0.5], [10.7, 10.7, 'geographic']), ('light geographic and visible range [4, 9, 10.4, 2.0, 2.0]', [4, 9, 10.4, 2.0, 2.0], [10.4, 10.4, 'luminous']), ('light geographic and visible range [2, 40, 15, 4.0, 6.0]', [2, 40, 15, 4.0, 6.0], [15.8, 15, 'luminous'])]]
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 fixtureActualExpectedOutcome
light geographic and visible range [3, 25, 18, 4.5, 1.0][8.9, 8.9, 'geographic'][14.7, 14.7, 'geographic']Failed
light geographic and visible range [3, 25, 10, 4.5, 1.0][8.9, 8.9, 'geographic'][14.7, 10, 'luminous']Failed
light geographic and visible range [9, 64, 23, 5.0, 5.0][14.2, 14.2, 'geographic'][22.9, 22.9, 'geographic']Failed
light geographic and visible range [1.5, 12, 20, 4.0, 0.5][6.5, 6.5, 'geographic'][10.7, 10.7, 'geographic']Failed
light geographic and visible range [16, 36, 20.8, 3.0, 3.0][14.3, 14.3, 'geographic'][20.8, 20.8, 'luminous']Failed
light geographic and visible range [4, 9, 10.4, 2.0, 2.0][7.2, 7.2, 'geographic'][10.4, 10.4, 'luminous']Failed
light geographic and visible range [2, 40, 15, 4.0, 6.0][9.1, 9.1, 'geographic'][15.8, 15, 'luminous']Failed

SHA-256 / 6e3ec8771eca2a3abd980db2b34841fe76a17abeaaf79e65eeebba619e9e261c

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 7 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.

Every case sharing this mechanism uses the same contract and the same repair, so this one record is held back for all of them.

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Verification & scope

A deterministic toy model with stipulated rules and constants; not certified hydrographic software or a substitute for official tide tables. 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 2026-09-29T14:48:09.512509+00:00.

Case digest / 6edb5ba4fe62aba1e817521f8c90d1ba97166435cbf1cde400714084b44f6960