This is my first long distance flight with the X. The take off point was at 7200 FT asl, the lake is 1000 feet bellow, temperature was 92F, I flew out about 2500 ft and down -250 ft. The telemetry reported minus altitude just fine. When I returned I set my altitude to +8 ft and flew straight back and arrived at +8 ft. Even with the high elevation and high temperature I did not notice any difference in performance. A bit nerve wracking since it would have been tough to retrieve in case of a mishap.