FA-69157 / Tide and marine navigation tables / Member archive

Tidal coefficient classification: Coefficient 70 is not classed as spring · case 02

Borderline spring tides are labelled mean.

Member previewVariant 2 · 3 implementations · 7 checks per implementation

Case contract

Input [hw, lw_before, lw_after, z0, U]: range = hw - mean of the two flanking low waters; coefficient = floor(100*(range/2)/U + 0.5) clamped to [20,120]. Class: exceptional if coef>=110, else spring if coef>=70, neap if coef<=45, else mean. Return [coef, class]. z0 (mean level) is informational only.

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
tidal coefficient classification [4.4, 1.6, 1.6, 2.9, 2.0]	`[70, "mean"]`	`[70, "spring"]`	Failed

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