In a south-pointing chariot, according to the hypothesis, Shaft B was connected to one road wheel and Shaft C was connected "through a direction-reversing gear" to the other road wheel. This made Shaft A rotate at a speed that was proportional to the "difference" between the rotation speeds of the two wheels. The pointing doll was connected (possibly through intermediate gears) to Shaft A. When the chariot moved in a straight line, the two wheels turned at equal speeds, and the doll did not rotate. When the chariot turned, the wheels rotated at different speeds (for the same reason as in an automobile), so the differential caused the doll to rotate, compensating for the turning of the chariot.