1. Hi There! I told you we
were at the record store!
This will be key to help
you understand how
error detection is applied
in the outside world.

2. I’m going to hand you
over to my friend Zack,
because he is an expert
on error correction!

3. Hi, I’m Zack. I heard
you want to know how
to apply error
detection and
correction in real life…

4. You see, Each record and
book we sell has an ISBN
number. This means that
we can check that the
items we ship to online
customers are correct.

5. Each book we sell has an ISBN (International
Standard Book Number). This means that each
book ordered by a customer online can be
checked before postage using this number. This
way our customers do not get the wrong item!

6. The ISBN number consists of 10 digits, this is
usually found on the back cover.
The tenth digit in the ISBN number is a check digit.
Just like the odd number of coloured cards was a
check technique in Raymondo’s Trick.

7. To ensure the we haven’t made a mistake we
check the checksum.
Here is how we work this out:
1. Multiply the first digit by ten
2. Multiply the second digit by nine
3. Multiply the third digit by eight
4. Multiply the forth digit by seven
5. Multiply the fifth digit by six
6. Multiply the sixth digit by five
7. Multiply the seventh digit by four
8. Multiply the eighth digit by three
9. Multiply the ninth digit by two

8. For example, for the ISBN number 4-23-914920-9 the
calculation would be:
(4x10) + (2x9) + (3x8) + (9x7) + (1x6) + (4x5) + (9x4) + (2x3) +
(0x2) =?
40 + 18 + 24 + 63 + 6 + 20 + 36 + 6 + 0 = 213
Then we divide the answer by 11
213 ÷11 = 110 r 2
Then we do 11 minus the remainder:
11-2= 9
Look back, is 9 the last digit of the ISBN? Yes!
If the last digit wasn’t 9 this would mean there would be a
mistake.

9. I hope that has helped! Keep
practicing and you will soon
get the hang of it!