e.g. to compute the expected check digit 7 for: 70651122?
digit  7  0  6  5  1  1  2  2  ?  

multiplier  1  2  1  2  1  2  1  2  
result  7  0  6  10 1 
1  2  2  4  horizonal sum = 23 
Note that the two digits of the multiplication results must be added before doing the sum.
Here is method more amenable to computer calculation:
e.g. to compute see if the check digit is as expected: 706511227
digit  7  0  6  5  1  1  2  2  7  

multiplier  1  z  1  z  1  z  1  z  1  
result  7  0  6  1  1  2  2  4  7  horizonal sum = 30 
This page is posted 
http://mindprod.com/jgloss/checkdigit.html  
Optional Replicator mirror

J:\mindprod\jgloss\checkdigit.html  
Please read the feedback from other visitors,
or send your own feedback about the site. Contact Roedy. Please feel free to link to this page without explicit permission.  
Canadian
Mind
Products
IP:[65.110.21.43] Your face IP:[34.207.146.166] 
 
Feedback 
You are visitor number  