OCR GCSE Computer Science Paper 2 Practice 2025 - Free Practice Questions and Study Guide

A check digit is a form of redundancy check used for error detection on numerical data. It is a single digit added to a string of numbers that is calculated from the other digits in the series. When data is entered, the system can recalculate the check digit using the same algorithm and compare it to the check digit that was entered. If they match, it confirms that the numerical data has likely been entered accurately. This method helps prevent data entry errors, such as transpositions or miskeyed numbers.

In contrast, a logic error refers to a mistake in the program's logic that leads to incorrect operation or output, which does not directly address the accuracy of numerical data entry. A format check ensures that data is in the correct format (like ensuring a date is entered as DD/MM/YYYY), but it does not verify the correctness of the numerical content itself. A performance test evaluates how well a system performs under certain conditions but does not focus on the accuracy of data entry. Thus, the check digit specifically targets verifying the accuracy of numerical entries.