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FA-69121 / Tide and marine navigation tables / Open access

Tide table zone time to UTC: Daylight time adds an hour to UTC · case 01

Summer tide times are two hours off in UTC.

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

ROOT CAUSE

The daylight hour is added to the offset instead of subtracted.

THE FAILURE

The daylight hour is added to the offset instead of subtracted.

Unsuccessful approach: Ignoring the daylight flag leaves summer tables an hour late.

Case contract

Input [local "YYYY-MM-DD HH:MM", zd, dst]: zone description zd in hours (positive west, may be fractional); UTC = zone time + zd, and when the table is on daylight time the clock is one hour ahead so UTC = local + zd - 1. Return UTC as "YYYY-MM-DD HH:MM" (24-hour).

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
import datetime
N = 1
observations = []
def solve(x):
    s,zd,dst=x
    dt=datetime.datetime.strptime(s,'%Y-%m-%d %H:%M')
    off=zd+(1 if dst else 0)
    u=dt+datetime.timedelta(minutes=round(off*60))
    return u.strftime('%Y-%m-%d %H:%M')
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('tide table zone time to utc ["2026-07-01 23:30", 4, true]', ['2026-07-01 23:30', 4, True], '2026-07-02 02:30'), ('tide table zone time to utc ["2026-03-14 06:12", 5, false]', ['2026-03-14 06:12', 5, False], '2026-03-14 11:12'), ('tide table zone time to utc ["2026-03-14 21:40", 5, false]', ['2026-03-14 21:40', 5, False], '2026-03-15 02:40'), ('tide table zone time to utc ["2026-07-01 00:20", -2, true]', ['2026-07-01 00:20', -2, True], '2026-06-30 21:20'), ('tide table zone time to utc ["2026-12-31 22:15", 3, false]', ['2026-12-31 22:15', 3, False], '2027-01-01 01:15'), ('tide table zone time to utc ["2026-01-01 01:05", -9.5, false]', ['2026-01-01 01:05', -9.5, False], '2025-12-31 15:35'), ('tide table zone time to utc ["2026-06-15 12:00", -5.5, false]', ['2026-06-15 12:00', -5.5, False], '2026-06-15 06:30')], [('tide table zone time to utc ["2026-07-01 00:20", -2, true]', ['2026-07-01 00:20', -2, True], '2026-06-30 21:20'), ('tide table zone time to utc ["2026-12-31 22:15", 3, false]', ['2026-12-31 22:15', 3, False], '2027-01-01 01:15'), ('tide table zone time to utc ["2026-01-01 01:05", -9.5, false]', ['2026-01-01 01:05', -9.5, False], '2025-12-31 15:35'), ('tide table zone time to utc ["2026-06-15 12:00", -5.5, false]', ['2026-06-15 12:00', -5.5, False], '2026-06-15 06:30'), ('tide table zone time to utc ["2026-06-15 12:00", 0, true]', ['2026-06-15 12:00', 0, True], '2026-06-15 11:00'), ('tide table zone time to utc ["2028-02-28 23:50", 1, false]', ['2028-02-28 23:50', 1, False], '2028-02-29 00:50'), ('tide table zone time to utc ["2026-09-10 13:45", -10, false]', ['2026-09-10 13:45', -10, False], '2026-09-10 03:45')], [('tide table zone time to utc ["2026-06-15 12:00", 0, true]', ['2026-06-15 12:00', 0, True], '2026-06-15 11:00'), ('tide table zone time to utc ["2026-06-15 12:00", -5.5, false]', ['2026-06-15 12:00', -5.5, False], '2026-06-15 06:30'), ('tide table zone time to utc ["2028-02-28 23:50", 1, false]', ['2028-02-28 23:50', 1, False], '2028-02-29 00:50'), ('tide table zone time to utc ["2026-09-10 13:45", -10, false]', ['2026-09-10 13:45', -10, False], '2026-09-10 03:45'), ('tide table zone time to utc ["2026-09-10 10:45", 3.5, true]', ['2026-09-10 10:45', 3.5, True], '2026-09-10 13:15'), ('tide table zone time to utc ["2026-05-05 05:05", 0, false]', ['2026-05-05 05:05', 0, False], '2026-05-05 05:05'), ('tide table zone time to utc ["2026-03-14 06:12", 5, false]', ['2026-03-14 06:12', 5, False], '2026-03-14 11:12')], [('tide table zone time to utc ["2026-09-10 10:45", 3.5, true]', ['2026-09-10 10:45', 3.5, True], '2026-09-10 13:15'), ('tide table zone time to utc ["2026-09-10 13:45", -10, false]', ['2026-09-10 13:45', -10, False], '2026-09-10 03:45'), ('tide table zone time to utc ["2026-05-05 05:05", 0, false]', ['2026-05-05 05:05', 0, False], '2026-05-05 05:05'), ('tide table zone time to utc ["2026-03-14 06:12", 5, false]', ['2026-03-14 06:12', 5, False], '2026-03-14 11:12'), ('tide table zone time to utc ["2026-03-14 21:40", 5, false]', ['2026-03-14 21:40', 5, False], '2026-03-15 02:40'), ('tide table zone time to utc ["2026-07-01 23:30", 4, true]', ['2026-07-01 23:30', 4, True], '2026-07-02 02:30'), ('tide table zone time to utc ["2026-07-01 00:20", -2, true]', ['2026-07-01 00:20', -2, True], '2026-06-30 21:20')], [('tide table zone time to utc ["2026-07-01 23:30", 4, true]', ['2026-07-01 23:30', 4, True], '2026-07-02 02:30'), ('tide table zone time to utc ["2026-03-14 06:12", 5, false]', ['2026-03-14 06:12', 5, False], '2026-03-14 11:12'), ('tide table zone time to utc ["2026-03-14 21:40", 5, false]', ['2026-03-14 21:40', 5, False], '2026-03-15 02:40'), ('tide table zone time to utc ["2026-07-01 00:20", -2, true]', ['2026-07-01 00:20', -2, True], '2026-06-30 21:20'), ('tide table zone time to utc ["2026-12-31 22:15", 3, false]', ['2026-12-31 22:15', 3, False], '2027-01-01 01:15'), ('tide table zone time to utc ["2026-01-01 01:05", -9.5, false]', ['2026-01-01 01:05', -9.5, False], '2025-12-31 15:35'), ('tide table zone time to utc ["2026-06-15 12:00", -5.5, false]', ['2026-06-15 12:00', -5.5, False], '2026-06-15 06:30')]]
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
tide table zone time to utc ["2026-07-01 23:30", 4, true]2026-07-02 04:302026-07-02 02:30Failed
tide table zone time to utc ["2026-03-14 06:12", 5, false]2026-03-14 11:122026-03-14 11:12Passed
tide table zone time to utc ["2026-03-14 21:40", 5, false]2026-03-15 02:402026-03-15 02:40Passed
tide table zone time to utc ["2026-07-01 00:20", -2, true]2026-06-30 23:202026-06-30 21:20Failed
tide table zone time to utc ["2026-12-31 22:15", 3, false]2027-01-01 01:152027-01-01 01:15Passed
tide table zone time to utc ["2026-01-01 01:05", -9.5, false]2025-12-31 15:352025-12-31 15:35Passed
tide table zone time to utc ["2026-06-15 12:00", -5.5, false]2026-06-15 06:302026-06-15 06:30Passed

SHA-256 / 5fa895d289c655e32500b8002ffcfa873be4e175da7c3d90c49b32121af5ee0d

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json
import math
import datetime
N = 1
observations = []
def solve(x):
    s,zd,dst=x
    dt=datetime.datetime.strptime(s,'%Y-%m-%d %H:%M')
    off=zd
    u=dt+datetime.timedelta(minutes=round(off*60))
    return u.strftime('%Y-%m-%d %H:%M')
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('tide table zone time to utc ["2026-07-01 23:30", 4, true]', ['2026-07-01 23:30', 4, True], '2026-07-02 02:30'), ('tide table zone time to utc ["2026-03-14 06:12", 5, false]', ['2026-03-14 06:12', 5, False], '2026-03-14 11:12'), ('tide table zone time to utc ["2026-03-14 21:40", 5, false]', ['2026-03-14 21:40', 5, False], '2026-03-15 02:40'), ('tide table zone time to utc ["2026-07-01 00:20", -2, true]', ['2026-07-01 00:20', -2, True], '2026-06-30 21:20'), ('tide table zone time to utc ["2026-12-31 22:15", 3, false]', ['2026-12-31 22:15', 3, False], '2027-01-01 01:15'), ('tide table zone time to utc ["2026-01-01 01:05", -9.5, false]', ['2026-01-01 01:05', -9.5, False], '2025-12-31 15:35'), ('tide table zone time to utc ["2026-06-15 12:00", -5.5, false]', ['2026-06-15 12:00', -5.5, False], '2026-06-15 06:30')], [('tide table zone time to utc ["2026-07-01 00:20", -2, true]', ['2026-07-01 00:20', -2, True], '2026-06-30 21:20'), ('tide table zone time to utc ["2026-12-31 22:15", 3, false]', ['2026-12-31 22:15', 3, False], '2027-01-01 01:15'), ('tide table zone time to utc ["2026-01-01 01:05", -9.5, false]', ['2026-01-01 01:05', -9.5, False], '2025-12-31 15:35'), ('tide table zone time to utc ["2026-06-15 12:00", -5.5, false]', ['2026-06-15 12:00', -5.5, False], '2026-06-15 06:30'), ('tide table zone time to utc ["2026-06-15 12:00", 0, true]', ['2026-06-15 12:00', 0, True], '2026-06-15 11:00'), ('tide table zone time to utc ["2028-02-28 23:50", 1, false]', ['2028-02-28 23:50', 1, False], '2028-02-29 00:50'), ('tide table zone time to utc ["2026-09-10 13:45", -10, false]', ['2026-09-10 13:45', -10, False], '2026-09-10 03:45')], [('tide table zone time to utc ["2026-06-15 12:00", 0, true]', ['2026-06-15 12:00', 0, True], '2026-06-15 11:00'), ('tide table zone time to utc ["2026-06-15 12:00", -5.5, false]', ['2026-06-15 12:00', -5.5, False], '2026-06-15 06:30'), ('tide table zone time to utc ["2028-02-28 23:50", 1, false]', ['2028-02-28 23:50', 1, False], '2028-02-29 00:50'), ('tide table zone time to utc ["2026-09-10 13:45", -10, false]', ['2026-09-10 13:45', -10, False], '2026-09-10 03:45'), ('tide table zone time to utc ["2026-09-10 10:45", 3.5, true]', ['2026-09-10 10:45', 3.5, True], '2026-09-10 13:15'), ('tide table zone time to utc ["2026-05-05 05:05", 0, false]', ['2026-05-05 05:05', 0, False], '2026-05-05 05:05'), ('tide table zone time to utc ["2026-03-14 06:12", 5, false]', ['2026-03-14 06:12', 5, False], '2026-03-14 11:12')], [('tide table zone time to utc ["2026-09-10 10:45", 3.5, true]', ['2026-09-10 10:45', 3.5, True], '2026-09-10 13:15'), ('tide table zone time to utc ["2026-09-10 13:45", -10, false]', ['2026-09-10 13:45', -10, False], '2026-09-10 03:45'), ('tide table zone time to utc ["2026-05-05 05:05", 0, false]', ['2026-05-05 05:05', 0, False], '2026-05-05 05:05'), ('tide table zone time to utc ["2026-03-14 06:12", 5, false]', ['2026-03-14 06:12', 5, False], '2026-03-14 11:12'), ('tide table zone time to utc ["2026-03-14 21:40", 5, false]', ['2026-03-14 21:40', 5, False], '2026-03-15 02:40'), ('tide table zone time to utc ["2026-07-01 23:30", 4, true]', ['2026-07-01 23:30', 4, True], '2026-07-02 02:30'), ('tide table zone time to utc ["2026-07-01 00:20", -2, true]', ['2026-07-01 00:20', -2, True], '2026-06-30 21:20')], [('tide table zone time to utc ["2026-07-01 23:30", 4, true]', ['2026-07-01 23:30', 4, True], '2026-07-02 02:30'), ('tide table zone time to utc ["2026-03-14 06:12", 5, false]', ['2026-03-14 06:12', 5, False], '2026-03-14 11:12'), ('tide table zone time to utc ["2026-03-14 21:40", 5, false]', ['2026-03-14 21:40', 5, False], '2026-03-15 02:40'), ('tide table zone time to utc ["2026-07-01 00:20", -2, true]', ['2026-07-01 00:20', -2, True], '2026-06-30 21:20'), ('tide table zone time to utc ["2026-12-31 22:15", 3, false]', ['2026-12-31 22:15', 3, False], '2027-01-01 01:15'), ('tide table zone time to utc ["2026-01-01 01:05", -9.5, false]', ['2026-01-01 01:05', -9.5, False], '2025-12-31 15:35'), ('tide table zone time to utc ["2026-06-15 12:00", -5.5, false]', ['2026-06-15 12:00', -5.5, False], '2026-06-15 06:30')]]
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
tide table zone time to utc ["2026-07-01 23:30", 4, true]2026-07-02 03:302026-07-02 02:30Failed
tide table zone time to utc ["2026-03-14 06:12", 5, false]2026-03-14 11:122026-03-14 11:12Passed
tide table zone time to utc ["2026-03-14 21:40", 5, false]2026-03-15 02:402026-03-15 02:40Passed
tide table zone time to utc ["2026-07-01 00:20", -2, true]2026-06-30 22:202026-06-30 21:20Failed
tide table zone time to utc ["2026-12-31 22:15", 3, false]2027-01-01 01:152027-01-01 01:15Passed
tide table zone time to utc ["2026-01-01 01:05", -9.5, false]2025-12-31 15:352025-12-31 15:35Passed
tide table zone time to utc ["2026-06-15 12:00", -5.5, false]2026-06-15 06:302026-06-15 06:30Passed

SHA-256 / 1e15d6e9cfef7a4019eff1d08f1e13152bb2bfeea34e80f775ee889be5b6ceb4

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 2026-09-29T14:48:08.568735+00:00.

Case digest / d9db486a948b0c916bcaa1be21cb2563e2bb7af228790dccb75e40280e4853b9