Computing the Check Digit of the ISBN

• Example: ISBN = 094001633

     Weighting Factors   10    9    8    7    6    5    4    3    2
     ISBN                 0    9    4    0    0    1    6    3    3
     Values (product)     0 + 81 + 32 +  0 +  0 +  5 + 24 +  9 +  6 = 157

• 157/11 = 14 with 3 remainder
• Check digit: 11 - 3 = 8
• The final ISBN is 0-940016-33-8.
• To check if an ISBN is valid, compute

     Weighting Factors   10    9    8    7    6    5    4    3    2    1
     ISBN                 0    9    4    0    0    1    6    3    3    8
     Values (product)     0 + 81 + 32 +  0 +  0 +  5 + 24 +  9 +  6 +  8 = 165

• The sum of the products must be divisible by 11 without remainder.
• Any single digit error can be detected with this method.