What is the antenna rotation axis?

This is the line around which the radar antenna rotates.  Usually, this line points straight up from the horizontal plane, and this fact is reflected by the parameter "Rotation axis: elevation above horizontal, in degrees = 90", set from the antenna plugin controls menu.  If you are operating a standard marine radar in its usual orientation, 90 is the correct value.  If you tilt the scanner on its side, then 0 degrees is the correct setting here.  Other settings are possible for some radar configurations.