hi guy,
i need te clear my doubt on this question.
user manual not did.
i'm flyig over a bridge, and start flying on surface at 0 meters, and waypoint is at -10 m, -20 m and so on to sidepass.
Margin os the exact value for set altitute under 0?
i'm making so experience with high pass, but moving on for side pass under flight level.
any guide or somethingelse to read and understand?
thanks

If i understand you correct, you want to fly to a waypoint which is -10m, -20m and so on, below your take off position.
You can not enter negative values in a GS Pro waypoint mission. (The minimum height is 1m)
You must start your aircraft from below the bridge and let the aircraft climb to the desired waypoint(s).