For those with a background in mathematics: The co-ordinate system used in oceanography is a left-handed co-ordinate system. Meteorologists, and physicists generally, use a right-handed co-ordinate system in which x points east, y north and z upward. The only difference between the two co-ordinate systems is a difference in the sign of some terms in the Equation of Motion discussed below. In the context of these notes this is of no relevance.