pulley in the intermediate idler position on stub shaft 39 it just so happens that as currently depicted in fig1 drive pulley 34 is a pulley with 24 teeth driven pulley 36 has 22 teeth and idler pulley 38 has 25 teeth again taking the example of fig1 when drive pulley 34 has 24 teeth and driven pulley 36 has 22 teeth as shown in fig1 this 24 tooth drive pulley 22 tooth driven pulley set up produces a first clip value u2014 i e the mower will move forward by a first predetermined distance in the time interval t 2 u2212 t 1 identified in the background of the invention section a second clip value can be easily derived in fig1 by switching the driven and idler pulleys so that driven pulley 36 is now the pulley with 25 teeth and idler pulley 38 is now the pulley with 22 teeth this reconfigured 24 tooth drive pulley 25 tooth driven pulley set up produces a second clip value u2014 i e the mower will move forward by a second predetermined distance in the time interval t 2 t 1 with the second distance being different than the first distance in this respect the reader hereof should remember that the ground speed of the mower as provided by the traction drive remains a constant but the time interval t 2 u2212 t 1 is different in the second instance so the mower travels a different distance in that different time interval t 2 u2212 t 1 leading to the new and different second clip value accordingly with the 24 tooth pulley in place as drive pulley 34 two clip values can be obtained depending upon which of the remaining two pulleys.