|I recently added a review on the industrial snap press, and someone suggested I share how I get the two sides of the finished snap to line up.
I try to make it as simple as possible. I always apply the snaps as a finishing touch, if I can. I don't pre-mark both sides of the item, just one side. I use the snaps applied to THAT side to mark the corresponding snap placement. I found if you mark both sides from the pattern markings, you might make one seam 1/4" shorter or longer--throwing off snap alignment. So, only mark one side!
I just apply all snaps to one side of the item--down the length of the item. I measure the snap placement individually fron the edge of the fabric, say to a uniform 1/2" or so. With practice, you can eyeball it.
Then I hold the finished snap side to the side that needs snaps. Just lay them down together on a flat surface, finished-snap side on the bottom, align seams, hems, ends--whatever works for your item. Then I feel the already applied snaps through the side that needs snaps (with some fabrics you can even see the snaps). With a vanishing marker, draw a line on the un-applied side right in the middle of the snap you can feel. This will give you snap placement markings that will exactly match both sides.
Hope this helps! (and isn't too confusing!)