Realisticly, if you were to put something on an elastic band at say, 5m (out of the 100m), and then stretched that same band another 100m, the thing would actually move forward past the original 5m to something else. If point A is at 50m on day 1 and you're given the amount it actually moves after stretching, let's say 10m per every 100m stretched, then point A would then be at 60m down the line. Point A didn't actually move on the band, but since you're STRETCHING the band, whatever is on it moves with the stretching aspect. You can actually test this. Take a tick rubberband and cut it in half. Put a push pin or a thumbtack in the middle and then stretch the band on one end. Meaning, keep one hand locked and then pull with the other. See where it ends up.