The table is indexed by latitude at 5-degree intervals; intermediate values are calculated using interpolation. Robinson did not specify any particular interpolation method, but it is reported that others used either Aitken interpolation (with polynomials of unknown degrees) or cubic splines while analyzing area deformation on the Robinson projection.[10] The X column is the ratio of the length of the parallel to the length of the equator; the Y column can be multiplied by 0.2536[11] to obtain the ratio of the distance of that parallel from the equator to the length of the equator.[3][4]