Another approach to the Lorentz Transformations. Relativists often use a quantity calledrapidity to describe the frame transformations. It is related to the speed factor (Beta) by (Beta) = f(R), where f is a hyperbolic function. The reason for using rapidity is that it is additive across reference frames. That is to say, if a particle has rapidity R in the unprimed frame, rapidity R' in the primed frame, and Rv is the rapidity of the primed frame to the unprimed frame, then R = R' + Rv. Using this fact, the velocity addition formula, and the addition formulas for hyperbolic functions, determine the function f(R).