2-1-2 Weighted MOD 10 Check Digit Calculation

Calculating the check digit for a MSI Bar Code.

Using the following example of 404079(6)
1. Drop the check digit and all start and stop digits. The number to be processed is: 404079
2. Multiply the rightmost digit and every alternate digit to the left by the number two (2):

4	0	4	0	7	9
X	2	X	2	X	2
_________________________________________
	0		0		18

3. Add the digits of the resulting numbers:
0+0+1+8=9
4. Add the product of step 3 to the digits not multiplied by 2:
4+4+7=15+9=24
5. In order to obtain the actual check digit, subtract the sum from the next highest number ending in zero:
30-24=6