MHD simulations give about the same dependence of transpolar potential on solar wind electric field (IEF) as the Hill model of transpolar potential, including saturation and dependence on ram pressure. In the Hill model, feedback of the region 1 current system is presumed to limit the rate of reconnection at the magnetopause thereby causing transpolar potential saturation. MHD simulations add as relevant information that in the saturation domain the region 1 current system usurps the role of the Chapman-Ferraro current system, which disappears. This means that the region 1 current system takes on the role of providing the current and generating most of the magnetic field in the J ¿ B force at the magnetopause that balances solar wind ram pressure. Viewed from this perspective, transpolar potential saturation results not from the region 1 current system limiting the rate of reconnection at the magnetopause but instead from ram pressure (more accurately, total solar wind stresses) limiting the total amount of current that can flow in the region 1 current system. Transpolar potential saturation is then the limit on transpolar potential that corresponds to the ram-pressure limit on total region 1 current.