Check Digits (Cambridge (CIE) IGCSE Computer Science)

Revision Note

Robert Hampton

Written by: Robert Hampton

Reviewed by: James Woodhouse

Check Digits

What is a check digit?

  • A check digit is the last digit included in a code or sequence, used to detect errors in numeric data entry

  • Examples of errors that a check digit can help to identify are:

    • Incorrect digits entered

    • Omitted or extra digits

    • Phonetic errors

  • Added to the end of a numerical sequence they ensure validity of the data

  • Calculated using standardised algorithms to ensure widespread compatibility

  • Examples of where check digits can be used include:

    • ISBN book numbers

    • Barcodes

ISBN book numbers

  • Each book has a unique ISBN number that identifies the book

  • A standard ISBN number may be ten digits, for example, 965-448-765-9

  • The check digit value is the final digit (9 in this example).

  • This number is chosen specifically so that when the algorithm is completed the result is a whole number (an integer) with no remainder parts

  • A check digit algorithm is performed on the ISBN number and if the result is a whole number, then the ISBN is valid

Barcodes

  • Barcodes consist of black and white lines which can be scanned using barcode scanners

  • Barcode scanners shine a laser on the black and white lines which reflect light into the scanner

  • The scanner reads the distance between these lines as numbers and can identify the item

  • Barcodes also use a set of digits to uniquely identify each item

  • The final digit on a barcode is usually the check digit, this can be used to validate and authenticate an item

Worked Example

Check digit algorithms are used to determine whether an error has occurred in transmitted data.

State the names of two examples of a check digit algorithm.

[2]

Answer

  • ISBN [1]

  • Barcode [1]

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Robert Hampton

Author: Robert Hampton

Expertise: Computer Science Content Creator

Rob has over 16 years' experience teaching Computer Science and ICT at KS3 & GCSE levels. Rob has demonstrated strong leadership as Head of Department since 2012 and previously supported teacher development as a Specialist Leader of Education, empowering departments to excel in Computer Science. Beyond his tech expertise, Robert embraces the virtual world as an avid gamer, conquering digital battlefields when he's not coding.

James Woodhouse

Author: James Woodhouse

Expertise: Computer Science

James graduated from the University of Sunderland with a degree in ICT and Computing education. He has over 14 years of experience both teaching and leading in Computer Science, specialising in teaching GCSE and A-level. James has held various leadership roles, including Head of Computer Science and coordinator positions for Key Stage 3 and Key Stage 4. James has a keen interest in networking security and technologies aimed at preventing security breaches.