You've tripped yourself on your math though. Summing is addition, not subtraction. By doing the equations the way you did (straight subtraction, as opposed to the addition of negative forces), you came the erronious conclusion that both mounting screws are in tension, with no forcing opposing, thereby resulting in the footbraces floating off into space as all the forces are in one direction with no opposition. The drawing is in fact correct in noting the left hand screw as being in compression. Try pinning the unit if screw tension is confusing you. When it's pinned, it becomes quite obvious. And, as the original person noted, the moment is force over distance. Be it the force of the foot over the distance of the pedal, or the forces of the screw over the length of the track.