The algorithms for calculating hydraulics and SS is based upon the work found in  and . The calculation is done by finding all geometrical points of interest. Locations where something change geometrically, ie. radius, inclination or eccentricity, is found and then a pressure drop calculation between each point is done using the fluid present in that section of the well. The calculation is done inside the drill pipe and inside the annulus. The drill bit is handled explicitly, and a common approach, as described in eg.  is used. This paper also discusses the coefficient of discharge used in the formula.