How to rotate a horizontal platform with left / right controls?

[GDS]

Hello all, I'm new here so please excuse any stupidity that I so happen to show. Anyway, I have gotten busy with a few tutorials so far, messing around with certain things, and I wanted to figure out how to

1) Rotate a horizontal platform (from its center), and then...
2) Allow the player to control that rotation, clockwise or counter-clockwise

The idea is to keep a ball on the platform and then by rotating the platform the ball slides in the direction the platform has been rotated. Thanks

[PlasmaVoid]

On Input(You can decide what this is, right key, left key etc):
-Set Angle(Platform) = Angle(Platform) + X. X is the amount(in degrees) to want to rotate the platform. This will rotate it to the left.
On Input(You can decide what this is, right key, left key etc):
-Set Angle(Platform) = Angle(Platform) - X. This will rotate it to the right.

[GDS]

Thanks for this. Just one thing, it doesn't seem like it is rotating right at the center of the object? My platform is 600 pixels long and 16 pixels thick, and yet when I rotate the platform the left end of it has a longer reach when it reaches the top of the rotation than the right end. Where can I find out the center that has been set for the object? Other editors I have tried in the past allowed you to simply click where ever on the object to set its center.... is there anything like that in fusion 2.5? Thanks

[GDS]

Ok, so I've figured out the action point of the object and increased the size of the platform by 1 pixel either way (to create a perfect center), to which I then set the action point dead center (300 of 601 and 8 of 17). I even drew a line going down the center of the platform so I can see if the rotation is correct. Yet when I rotate the platform I can see the rotation point is off to the left. It actually looks like the platform is rotating around a circle and not at its center.

EDIT: Never mind, figured it out.