Use this window to control how different magnitude stars are to appear. Magnitude (a.k.a. relative magnitude) refers to how bright a star appears. This is an inverse relationship: the lower the magnitude, the brighter the star. Very bright stars have magnitudes less than zero.
The "Limiting magnitude" drop-down listbox determines how bright a star must be before it can be displayed.
The two sliders control what size dot is used to represent the brightest and dimmest stars. The "Dimmest" slider refers to stars having a magnitude indicated by the value specified by "Limiting magnitude".
Pressing "OK" accepts new values.
Pressing "Cancel" rejects any changes.