In the past when I’ve set up a dado blade, I picked out the chippers I thought would get me close and then made the fine adjustments by taking them back off the saw to add the shims. The jig you see here makes the set-up much easier by allowing me to make these adjustments before installing the stack on the saw.
To use the jig, I simply lay a scrap piece along the stack and then add chippers and shims so the teeth are flush with the scrap. Snug down the wingnut to compress the stack.
Once you get it right, you can transfer the stack to the saw.