[amsat-bb] G-5500 Orientation

I am installing a G-5500 Elevation rotor and trying to determine orientation of elevation with reference to software specifically rtrcontrold for Linux but I'd suspect this would be typical to most PC applications. If a sat is 45 degrees above horizon should rotor control read 45 or 135 degrees on the hardware control dial? What I'm asking is when I want to mount antenna where 90 degrees is horizontal or vertical? It seems natural that midway point is horizontal but midway point is 90 degrees. I don't think I ever have a reason to point antenna into the mud so it makes most sense that midway 90 degrees is straight up??