ISBN Calculations (Check Digit)

During the design stage, the designer has to limit the chances of inaccurate data. Therefore, validation checks have to be established. These checks include:-

1) Range Check: Checks whether data is within acceptable boundaries.

2 ) Length Check: Checks if the data is entered with the required number of characters

3) Character Check: Checks that the data entered doesn't include invalid characters

4) Picture Check: Checks that data is entered in a specific format.

5) Limit Check: Similar to "Range Check", only it has one boundary.

6) Presence Check: Checks that data is actually present.

7) Consistency Check: Checks that data field tie up with each other

8) Check Digit: Performs complex calculations on a range of numbers, then compares them with the check digit. (We'll go into this more deeply with the ISBN calculations)

 

1. Take the first 12 digits of the 13-digit ISBN
2. Multiply each number in turn, from left to right by a number. The first digit is multiplied by 1, the second by 3, the third by 1 gain, the fourth by 3 again, and so on to the eleventh which is multiplied by 1 and the twelfth by 3.
3. Add all of the 12 answers.
4. Do a modulo 10 division on the result from step 2. (Don't know what a modulo 10 division is? It's easy. It's just the remainder from a whole number division by 10. I bet you learned to do that in junior school, before you even learned about decimal fractions.)
5. Take that remainder result from step 4.If it's a zero, then the check digit is zero. If the remainders isn't zero then subtract the remainder from 10. The answer to that is your check digit.

 

Let's take #9781861972712# as an example:-

9 x 1 = 9
7 x 3 = 21
8 x 1 = 8
1 x 3 = 3
8 x 1 = 8
6 x 3 = 18
1 x 1 = 1
9 x 3 = 27
7 x 1 = 7
2 x 3 = 6
7 x 1 = 7
1 x 3 = 3

Add the results 

9 + 21 + 8 + 3 + 8 + 18 + 1 + 27 + 7 + 6 + 7 + 3 = 118 

Modulo 10 the result

118 modulo 10 = 110 remainder 8

Work out the digit

8 doesn't equal zero, so check digit = 10 - 8 = 2