Primary strength calculations generally consider the midships cross section of the ship. These calculations treat the whole ships structure as a single beam, using the simplified Euler–Bernoulli beam equation to calculate the strength of the beam in longitudinal bending. The moment of inertia (technically, second moment of area) of the hull section is calculated by finding the neutral or central axis of the beam and then totaling up the quantity formula_1 for each section of plate or girder making up the hull, with formula_2 being the moment of inertia of that section of material, formula_3 being the width (horizontal dimension) of the section, formula_4 being the height of the section (vertical dimension), formula_5 being the area of the section and formula_6 being the vertical distance of the center of that section from the neutral axis.