# CheckdigitDamm ( digitSequence )

Calculates a check digit using the Damm algorithm

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Jeremy Bante Beezwax Datatools, Inc. http://beezwax.net |

CheckdigitDamm ( 12345 ) ;

12345 & CheckdigitDamm ( 12345 ) ;

CheckdigitDamm ( 12345 & CheckdigitDamm ( 12345 ) )

)

123459

0

Function definition: (Copy & paste into FileMaker's Edit Custom Function window)

Calculates a check digit to append to a digit sequence that can be used to validate that the digit sequence has been transcribed correctly.

This custom function implements an algorithm described by H. Michael Damm in 2004.

## Comments

Mark Scott, San Francisco Jan 9, 2015 |
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Excellent! The Damm algorithm is, AFAIK, the most robust one out there for a single-numeric-digit check digit scheme. It's able to detect all single-digit transcription errors (e.g., 6↔9) and all adjacent transpositions (e.g., 47↔74)—which together account for 90% of errors—and most (though not all) of the other common errors, such as jump transpositions (e.g., 358↔853), twin errors (e.g., 44↔66), and jump twins (e.g., 494↔797). Additionally, it detects all English-language phonetic errors (e.g., 16↔60). The older and more widely known Luhn algorithm misses the transposition 09↔90—yikes! those digits are right next to one another on any keyboard without a dedicated numeric keypad (think laptop!)—as well as the twin errors 22↔55, 33↔66, and 44↔77. Yikes, again! Those three pairs are each vertically adjacent on a numeric keypad. I was about to code this myself, then decided to check here to see if someone has saved me from reinventing the wheel. Thanks, Jeremy; good work! Mark |
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