 For this example, we'll start with a couple of small numbers, say, 10 minus 7. So 10 in binary is, and 7 is, so I'm going to end up doing some borrowing this time. Because, well, 0 is less than 1, so I can't do 0 minus 1, really. I need to come over to the next place, borrow something. So I can do 10 minus 1. So I'll borrow this 1 from here, leaving me with 0. Now I've got a 10 here, so 10 minus 1 leaves me with 1. Now I've got a 0 minus 1, same thing. So I'm going to have to come over here and borrow something. But I don't have anything here, so I need to come over to the next position and borrow something. So this is now 0. Now I've got a 10 here, but I still need to borrow something from this place. So 10 minus 1 leaves me with 1, and now I have a 10 in this position. So 10 minus 1 is 1, and 1 minus 1 is 0. So we started with 10, we subtracted 7, and we're left with 3 in binary. If I use these same numbers in octal, I'd have 12 for my 10. I would subtract off 7. And now I'd say, well, 2 is less than 7, so I can't do 2 minus 7. I need to borrow something. So I borrow this 1. Now I've got 12 minus 7. And I can do this a couple of different ways. I can say, oh yeah, this is really an 8. 8 plus 2 is 10. 10 minus 7 is 3. I know that one. Or I can say, well, really, 7 didn't go into 2. So maybe I should just subtract the 7 from the 10. So 10 minus 7 leaves me with 1 in octal. And then I can do 1 plus 2 gives me 3 as well. So in both cases, I end up with 3. For another example, I might take 13 minus 7. 13 in binary is, and 7 is still 1, 1, 1. So if I do this subtraction, 1 minus 1 is 0. 0 minus 1, well, I'll need to go borrow something again. So I borrow something from the next position over. Now I've got 10 minus 1, which leaves me with 1. Now I've got a 0 minus 1 again. So I will borrow something from this position. Now I've got a 10 minus 1, which leaves me with 1. And 0 minus, nothing, is also 0. So I get a binary 6, which is what I expect. Octal version, I've got 15 for my 13. And then 7 is still 7. So first thing is to just write down 8 the way you're used to. But again, we could say, well, 10 minus 7 is 1. So 1 plus 5 is 6. Or I can do 8 plus 5 is 13. Minus 7 is 6. 6 in octal is also 6. So either of those will get me to the 6 that I expect. And in this case, I do get 6, since that is a valid number in octal.