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Here is what the guy who fitted my slotted caged-quill pedal cleats used on me 30 years ago:

The New England Cycling Academy Fit Kit, with its R.A.D. (Rotational Adjustment Device)

He had me bring my bike in and checked out my fit on that first of all. Then he had me spin on it (I don't remember the setup. It was 30 years ago). He had some attachments on my feet with rods that came out the side. When your cleat fit your toe out the rods would rotate straight instead of arcing. It took several adjustments to get my right side correct. I had to look straight ahead as if I were riding on the road so I didn't even get to see any of this while I was pedaling.

It worked exactly right in fitting those cleats. I'm not saying that's the only way to do it but it sure saved me from a lot of trial and error.

I had to laugh at Sheldon Brown's version of toe out. I could show him what toe out really is.