mod11

mod11 refers to a checksum algorithm used for data validation. It is a simple but effective method for detecting single-digit errors, transpositions of adjacent digits, and other common transcription mistakes. The algorithm works by assigning a specific weight to each digit in a number and then calculating a weighted sum. This sum is then divided by 11, and the remainder is used to derive a check digit.

The process typically involves multiplying each digit of a number by a sequence of weights, often starting from 2 and increasing. The sum of these products is then taken modulo 11. The result of this modulo operation is then subtracted from 11. If the result is 10, it is usually represented by a specific character, such as 'X'. Otherwise, the result is the check digit itself.

When validating a number, the entire number, including the check digit, is subjected to the same weighted sum calculation. This calculated check digit is then compared to the check digit provided. If they match, the number is considered valid. If they do not match, it indicates an error in the data. mod11 is commonly found in identification numbers, account numbers, and other systems where data integrity is important. Its simplicity and effectiveness make it a popular choice for basic error detection.