I have students set up a base sheet before they do the first color run. I
have them set their block on scrap paper and make 90 degree corners out of
thin poster board or something similar and tape it to the scrap paper so
they can set the block back in the same spot each time. Then measure for the
paper and set 90 degree corners at the top for the printing paper so that
it's set in the same spot each time as well. Hope it makes sense, much
easier if I could draw an example. I'm visual ,dang it.