If we place two detectors at the same angle from the target, one on the right and one on the left, they will generally measure a different number of electrons  and . Consequently it is possible to define the asymmetry , as
The Sherman function  is a measure of the probability of a spin-up electron to be scattered, at a specific angle , to the right or to the left of the target, due to spin-orbit coupling. It can assume values ranging from -1 (spin-up electron is scattered with 100% probability to the left of the target) to +1 (spin-up electron is scattered with 100% probability to the right of the target). The value of the Sherman function depends on the energy of the incoming electron, evaluated via the parameter . When , spin-up electrons will be scattered with the same probability to the right and to the left of the target.
Then it is possible to write
Plugging these formulas inside the definition of asymmetry, it is possible to obtain a simple expression for the evaluation of the asymmetry at a specific angle , i.e.:
Theoretical calculations are available for different atomic targets and for a specific target, as a function of the angle.