They are referring to the rest mounting holes, once commonly referred to as Burger Button Holes. And it's not Burger Button. It's Berger named after Vic Berger who was the inventor of the Berger Button, a spring pressure button mounted through the riser to dampen sideways oscillation of the arrow when shot with fingers. There are still lots of them made, but release shooters don't use them. They are commonly called plunger buttons.
Everybody has some notion that a rest has to be set so the arrow bisects the rest mounting holes, but it isn't so. If the rest is high or low then the nocking point on the string is located accordingly during any tuning process. That's partly what tuning is all about. Years ago the deepest part of the grip was the vertical center of the bow and we were able to finely tune those bows. Even with today's bows the rest is above center on almost all models and the vertical center is closer to the arrow shelf, which isn't even an arrow shelf anymore because we don't shoot arrows off the shelf.
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