In a two-dimensional statics problem involving finding a moment about a point, I don't understand how the result is either in the positive/negative z direction. I realize moments are found by the cross product, and the cross product requires the answer to be perpendicular to the plane that the two vectors form. If I look down at the surface of my desk and take that to be an x-y plane. a pencil laying on the plane is held stationary at it's left end, and the right end is made to rotate clockwise. This tells me that I can expect my moment to be in the negative z direction (say, going down through the surface of the desk). This makes no sense to me, what concept am I missing here?