The adjustable one is the Declination adjustment, to give the dish a little bit of "tilt" to better follow the arc wherever the dish is installed. It's a set and forget setting, depending on the installation location.
Depending on manufacturer, it can be located at the top OR bottom of the dish. Your photo isn't sharp enough for me to tell which one it is on this dish.
Also, NO, it is NOT the same as the Elevation adjustment, which is the one in the bottom "V" area.