Check Digit

LEARNING OBJECTIVES:

The specification states - you should be able to:

understand the purpose of the following data validation methods: check digits; and batch totals (hash and control);

Check Digit Explained

Check Digit

Some information systems process data that is entered into them in batches from documents. These systems typically use batch processing.

5 steps of modulus 11 check digit calculation

Each digit is given a weighting.
Each digit is multiplied by its weight.
The sum is calculated.
The total is divided by 11 and the remainder is obtained.
The remainder is subtracted from 11.

What is meant by the weighting of a digit?

It’s position/place within the data value.

Special cases

If remainder is 1 or 0, the result will be 10 or 11.
If remainder is 1 (or the result is 10) the check digit becomes X.
If remainder is 0 (or the result is 11) the check digit becomes 0.

Worked examples

Explain how a check digit will detect a transposition error

If two digits are interchanged.
The weightings will change.
Therefore, the check digit calucation will be incorrect.

Effectiveness of a check digit in detecting data entry errors

A check digit can detect most transposition errors.
If the positions of two digits change, their weightings and the products will change.
This will usually cause the check digit to be incorrect and the error will be detected.
Some transposition errors may not be detected.
A check digit can detect when a single incorrect digit is entered.
If a single incorrect digit is entered, the product will change.
This will cause the check digit to be incorrect and the error will be detected.
Multiple incorrect digits may not be detected.

Past Paper Questions

Check Digit Past Papers.pdf

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