Some cars have variable-ratio steering, which uses a rack-and-pinion gear set that has a different tooth pitch (number of teeth per inch) in the center than it has on the outside.

However, after shaved by shaving cutter with true involute profiles, there are the "mid-concave" phenomena on the pitch points of shaved gear tooth profiles inevitably.

This paper presents a practical method to calculate the pressure angle at pitch cylinder, of gear drive with computer.