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 FileMaker Pro Custom Functions

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CheckdigitDamm ( digitSequence )

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  Average rating: 5.0  (23 votes)
  Discuss this Custom Function

Jeremy Bante, Beezwax Datatools, Inc.

Calculates a check digit using the Damm algorithm

Sample Input:
List (
CheckdigitDamm ( 12345 ) ;
12345 & CheckdigitDamm ( 12345 ) ;
CheckdigitDamm ( 12345 & CheckdigitDamm ( 12345 ) )
Sample Output:

 Then copy & paste into FileMaker Advanced'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.

Note: these functions are not guaranteed or supported by Please contact the individual developer with any questions or problems.

This is my Custom Function and I want to edit it


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 Scott, San Francisco
January 09, 2015 12:53pm

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