Which pass do you look at for Radix Sort stability?

Question

I know this is a fairly poorly worded question, but I can't think of a better way to phrase it in the title.

So in Radix Sort, you go digit by digit from least significant to most significant, and along the way you are swapping elements around. When considering the case where two digits are the same, do you look at the original array to decide which should come first, or do you look at the previous iteration?

In one case you would have to store the original to look back on, so my guess is it's not that, but I can't tell which provides the correct result by my own examples. Let me know if I need to describe my question better and I will try.