FA-96142 / Postal address normalization / Member archive

Delivery point check digit: a zero check digit becomes 10 · case 02

Codes whose digit sum is a multiple of ten end in "10".

Member previewVariant 2 · 3 implementations · 7 checks per implementation

Case contract

Input [zip5, plus4, primary]. The delivery point is the last two of the leading digits of the primary number, zero-padded to two, or "99" when there are none. With a plus-four the digit string is zip5 + plus4 + delivery point, otherwise zip5 alone. Append the check digit (10 - digit sum mod 10) mod 10.

Why this case matters

A wrong delivery point or check digit sends machine-sorted mail to the wrong door or rejects it.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
three-digit house number	`"2344267892310"`	`"234426789230"`	Failed

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