Kerouac drifting off

I've just been marvelling at Jack Kerouac's original scroll draft of On the Road, on display at the British Library in a special looooooooong display case. (It doesn't display the whole 120 feet, but a large portion of it, with the rest rolled at one end.) 

It's impressive to see it, but there's one thing I don't understand.  Every source I've ever seen says that Kerouac taped tracing-paper together to form the scroll so he wouldn't have to be distracted by changing paper in the typewriter.  But at regular intervals all the way along, probably equivalent to about 2-3 sheets  of ordinary paper, a neat shift occurs in the margin.  Seems his typewriter was typing crooked, and when the text block drifted too far over he had to stop what he was doing, raise the bar that locks the paper in place, and shove the whole thing over a bit before clamping it back down and carrying on.

So - how is that not distracting?  I think I'd find it even more so, as you'd end up constantly monitoring how far you were floating off to the side.

Am I interpreting what I'm seeing correctly?  Or does anyone know a better explanation of these breaks?