1 72 THE OLIVER PLOW BOOK 



wheel on the ground. However, it is easy to imagine a 

 hard plowing condition where the plow depth would 

 remain the same and the effect show on the tractor. 

 But remember that whatever happens to the plow or 

 tractor, the draft line straightens. 



Suppose the plow at point, C, requires 550 pounds 

 effort to move ahead, and the tractor can only produce 

 525 pounds effort. In this case the plow would remain 

 stationary and point, B, the center of power of the 

 tractor, would lower until it reached the line AHC, 

 providing no outside influence stopped it. If point, B, 

 were back of the center of power the front wheels of the 

 tractor would rise. If point, B, were ahead of the 

 center of power undue weight would be brought to bear 

 on the front trucks, and the rear wheels of the tractor 

 would tend to slip because of the tendency to relieve 

 them of weight. When this condition occurs, as it often 

 does, the operator must adjust the hitch on both the 

 plow and tractor until the draft line is straight. 



It is further apparent that the height of the hitch on 

 the tractor and the range of clevis adjustment on the 

 front of the plow have everything to do with keeping 

 this line straight when plowing at different depths. 



Theoretically speaking, a different adjustment should 

 be made on a vertical clevis every time the plow depth 

 is to be changed, but from the way plows are designed, a 

 slight variation in depth can be made without materially 

 affecting the draft line. However, one should be very 

 careful when adjusting the plow depth to vary it as 

 little as possible if he expects his plow to operate per- 

 fectly. 



Another feature of the vertical adjustment is shown in 

 Fig. 5. The lines, AHC and BGC, show that the different 



