ITPEC IP October 2018 Question 3

Which of the following is an appropriate purpose of appending a check digit to a customer code?

a)To check the customer code for input errorsb)To arrange customers in the order of acquisition when a list of customers is createdc)To enable customers to be inferred easily and quicklyd)To enable the grouping of customers by geographical area or other attributes

Explanation

To check the customer code for input errors — the check digit is computed from the other digits, so a mistyped code no longer matches it.

When a code is issued, a fixed calculation (for example, a weighted sum of the digits taken modulo 10 or 11) is applied to its digits and the result is appended as the last digit. When the code is entered, the system repeats the calculation and compares the result with the entered check digit. A mismatch shows that a digit was mistyped or two digits were swapped, and the input is rejected before it reaches the data.

Answer (a)

Why not others:

•(b) — ordering customers by acquisition is done with a sequence code, serial numbers assigned in order; a check digit says nothing about when the customer was acquired
•(c) — a code that lets the customer be recognised at a glance is a mnemonic code, such as letters taken from the name; a check digit carries no meaning
•(d) — grouping by area or another attribute needs a classification (group) code, in which part of the code stands for the attribute

Key rule: A check digit adds no information about the customer; it is redundancy that lets the computer detect a code keyed in wrongly.

Basic Theory · AI-written, may contain errors

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