What type of error will a modulus-11 check digit detect?

A modulus-11 check digit is specifically designed to detect single transposition errors, which occur when two adjacent digits in a number are swapped. The calculation of the check digit takes each digit's position and its numerical value into account, allowing it to validate that the digits appear in the intended sequence.

In the context of error detection, a single transcription error, which involves changing one digit to another, would not necessarily affect the computed check digit in a predictable way, as the relationship between the digits can vary significantly based on their positions. Conversely, multiple errors could lead to a situation where the check digit still appears valid, as it is possible that the combined effect of various changes might not breach the established modulus. Thus, the modulus-11 system is particularly effective at identifying transposition errors while not being solely reliable for other types of mistakes.