There's, what appears to be, two adjustable flow restrictors residing below the skimmer basket.
One is mounted on the under side of a removable plate and sits on the bottom of the skimmer box. It also appears to have a float valve in it presumably to block off the skimmer if the water level drops below the inlet. The other one is "built-in" to the skimmer itself.
My questions are simply; what are they for and, how do I know if they are adjusted properly?