IBM 3741 Data Station Reference Manual page 62

For example:
56
Basic number
Units position and every
alternate position of
basic number
Multiply
Digits not multiplied
Add
Next higher number ending
in
0.
Subtract
Self-check digit
6 2
4
8
6 2 8
12 4 16
4
1+2+1+4+4+1+6=19
20.
-19
Modulus 11
To compute modulus 11, do the following:
1.
2.
3.
4.
5.
Assign a weighting factor to each digit position of the
basic number. These weighting factors are 2-7,2-7,
etc. starting with the units position of the number,
excluding the self-check digit, and progressing
toward the high-order digH.
Multiply each digit by its weighting factor.
Add the products.
Divide this sum by 11.
Subtract the remainder from 11.
The difference is the self-check digit.
For example:
Basic number
2 3 4 5
Weighting factors 6 5 4
3
2
Multiply
6 10. 12 12
10.
Add
6+10.+12+12+10.=50.
Divide 50711=4 plus a remainder of 6
Subtract 11-6=5
Self-check digit
5