If you reverse the paddle arms, the screws in the clamps no longer drop into the little indexing dents in the crossbar. That lets you set the angle in a fully-adjustable way, to get that last tenth-degree just right. Doesn’t matter so much with the diamond plates since they’re all the same thickness (more or less) but when you start using non-standard paddles (like the waterstones) you need to be able to make that adjustment to keep the angle identical.
