Question related to maths numbersystem

We do two sums (the odd numbered digits and the even numbered digits), subtract one sum from the other, and see if this is divisible by 11. By the way, if we end up with zero, then that is divisible by 11. We can repeat that process, just as we did with 3. Let's look at an example:

70356

7+3+6=16

0+5=5

16-5=11

Is divisible by 11

We can, of course, do the summing in different orders. In fact we can just go from left to right adding and subtracting alternate digits: 7-0+3-5+6=11(divisible by 11).