FA-69119 / Tide and marine navigation tables / Member archive

Tide table zone time to UTC: Zone description is subtracted · case 04

UTC times are off by twice the zone description.

Member previewVariant 4 · 3 implementations · 7 checks per implementation

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.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
tide table zone time to utc ["2026-07-01 00:20", -2, true]	`"2026-07-01 01:20"`	`"2026-06-30 21:20"`	Failed

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