In terms of the direction of these parts spinning, the negative number is correct. The nomograph will verify that, as will the diagram. Try to visualize the ring and the sun spinning in the same direction without moving the planets and you'll strip your gears. You can see them spinning in the same direction by positioning both sliders at the same level. So it's sort of a question of semantics, but that would be fixed by indicating on the diagram which direction charges and which draws current from the battery. I do want to also incorporate a feature that will tell us whether MG1 is charging the battery or drawing power. One thing I don't know about that part is if MG1 can be allowed to spin freely in either direction without drawing a current... I'm also not sure if the directions of MG1 are tied to charge/discharge, or if it can do both in either direction. More homework!