The orientation of a bond, i.e. the direction of the half arrow, denotes the direction of positive power. An element with an incoming bond consumes power when the product of effort and flow is positive. For R, C and I-elements an incoming bond is the standard orientation. For sources the standard orientation is outgoing, because a source supplies power to the rest of the system. For the TF and GY-element the standard orientation is one incoming bond and one outgoing bond, since this reflects the natural flow of power. For the other bonds in a model, as much as possible an orientation from source to load is applied.