*Also, the banks may close a branch and remove it from this master list of BSBs.*

Its check digit is generated the same way as the UPC except that the even digits are multiplied by 3 instead of the odd digits.

EAN (European Article Number) check digits (administered by GS1) are calculated by summing each of the odd position numbers multiplied by 3 and then by adding the sum of the even position numbers.

The digit the farthest to the right (which is multiplied by 1) is the check digit, chosen to make the sum correct.

It may need to have the value 10, which is represented as the letter X.

In choosing a system, a high probability of catching errors is traded off against implementation difficulty; simple check digit systems are easily understood and implemented by humans but do not catch as many errors as complex ones, which require sophisticated programs to implement.

A desirable feature is that left-padding with zeros should not change the check digit.

A very simple check digit method would be to take the sum of all digits (digital sum) modulo 10.

This would catch any single-digit error, as such an error would always change the sum, but does not catch any transposition errors (switching two digits) as re-ordering does not change the sum.

A slightly more complex method is to take the weighted sum of the digits, modulo 10, with different weights for each number position.

To illustrate this, for example if the weights for a four digit number were 5, 3, 2, 7 and the number to be coded was 4871, then one would take 5×4 3×8 2×7 7×1 = 65, i.e.

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