FA-68845 / Tide and marine navigation tables / Member archive

Rule of twelfths: Per-hour twelfths are used as cumulative fractions · case 05

Mid-flood heights stay far too low and the tide never reaches high water.

Member previewVariant 5 · 3 implementations · 7 checks per implementation

Case contract

Input [t1,h1,t2,h2,t] in hours/metres for consecutive turning points t1<t2 (rise or fall). The interval is split into six equal tide hours with cumulative twelfths 0,1,3,6,9,11,12 and linear interpolation inside a tide hour. Return height rounded to 4 decimals, or None when t2<=t1 or t lies outside [t1,t2].

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
rule of twelfths [0, 0.5, 6, 4.1, 5]	`1.1`	`3.8`	Failed

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