The first task is determine the elements of the B matrix. We have:

where X₁₂ = cosq and Y₁₂ = sinq. B_x1 = cosq and B_x2 = -cosq, B_y1 = sinq and B_y2 = -sinq, for the 1-2 coordinate and since X₂₃ = 1 and Y₂₃ = 0 we have B_x2 = 1 and B_x3 = -1, for the 2-3 coordinate.

Given the above values we have for the angle coordinate B_x1 = -sinq/r₁₂, B_x3 = 0 and B_x2 = sinq/r₁₂. We also calculate B_y1 = cosq/r₁₂, B_y3 = -1/r₂₃, and therefore B_y2 = 1/r₂₃ – cosq/r₁₂.