Addition Errors

Extra characters are accidentally inserted into the data.

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Extra characters are accidentally inserted into the data.

Addition errors occur when extra characters are accidentally inserted during data entry. This can happen from double-tapping keys, misreading source data, or accidentally hitting adjacent keys. The result is a longer string than the original. Like omission errors, these can be quickly detected by checking length.

Original: ABCD → Error: ABCXD (X inserted)

12345 → 123345 (extra 3 inserted)
SMITH → SMIITH (extra I inserted)
AB-1234 → AB-12334 (extra 3 inserted)

How to recognize it

Copy is longer than original
Contains all original characters plus extras
Often a repeated or adjacent character

Common mistakes

Not noticing the length difference
Missing subtle additions in long strings
Confusing with doubled legitimate characters

Step-by-step walkthrough

Find the error: Original '12345' vs Given '123345'

Check lengths: original has 5 characters, given has 6
Compare position 1: '1' = '1'
Compare position 2: '2' = '2'
Compare position 3: '3' = '3'
Compare position 4: '4' vs '3' - extra character found
An extra '3' was inserted at position 4

Answer: Addition error: extra '3' inserted at position 4

Practice guidance

Error Checking