Because you have to multiply the last number by 1, the second to last by 2, etc. 
 $sum += (substr($account, $_-1, 1) * $_);

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multiplies the first by 1, the second by 2 (the wrong way around :)

In reply to Re: Re: Elfproef (Dutch bank account check) by Treenaks
in thread Elfproef (Dutch bank account check) by Treenaks

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