Answer:
If the global axis Z points downwards, this definition applies:
"Bottom" is on the side of the surface from which the positive local z-axis points, and "top" is the one in the direction of the negative local z-axis. (Please note: Notation of the global axis Z and the local surface axis z.)
If the global axis Z points upwards, the definition is reversed:
The bottom reinforcement lies on the side of the negative local surface z-axis, the top reinforcement accordingly on the side of the positive surface z-axis.
The local surface axes can be displayed in the Display navigator via Model → Surfaces → Surface Axis Systems x,y,z.
You can quickly change the z-axis of the surface: Right-click the surface. Then, select Reverse Local Axis System in the shortcut menu. This way, you can, for example, unify the reinforcement layers of walls.
We recommend orienting the global Z-axis downwards when creating the model. This ensures that the local z-axes for surfaces in the XY plane automatically point downwards, and thus the bottom reinforcements also rest on the bottom side of the surfaces.