Append a fourth check digit to each seven-digit code created by the Venn diagram method c₄= a₁ + a₂ + a₃ + a₄. With this additional check digit, can double errors be detected and corrected?

Question

Quizplus · Accepted Answer

By adding a fourth check digit, the resulting code will have eight digits. Since the Venn diagram method produces codes with three check digits, this means that the fourth check digit is calculated from the previous three. This makes it possible to detect and correct double errors, because if two digits are incorrect, the fourth check digit will not match the calculated value, indicating that an error has occurred.

Append a Fourth Check Digit to Each Seven-Digit Code Created