Commonly 35mm leaders have various frames that lend themselves for use as reference images during optical printer alignment. An example is this colour by deluxe graphic where the circle is a handy shape to see macro degree as well as left and right shift, etc.
Its worth mentioning that the pins in the camera gate can only acccomodate 35mm, but, once 1:1 macro is set up, then it doesnt matter what gates go in afterwards as it will still be 1:1.
