When using the moment-area method to find the deflection of a beam, how does the location of the tangent reference point specifically affect the direct calculation of the relative rotation between two points?

When using the moment-area method, the first moment-area theorem states that the relative rotation (or change in slope) between the tangents at any two points on the elastic curve of a beam is equal to the area under the M/EI diagram between those two points. Here, M is the bending moment and EI is the flexural rigidity of the beam. The tangent reference point is one of the two chosen points on the elastic curve whose tangent serves as the baseline or zero-angle reference for measuring the rotation of the tangent at the other point. Its location specifically affects the direct calculation of relative rotation in the following ways: Firstly, the chosen tangent reference point directly define....