Watt's Parallel Straight-line Mechanism
Move the Point A and observe the straight line trajectory for the point P
-L2=L4
-L1>L2=L4>L3
-Move the point A (Blue Point) and check the straight line trajectory of the point P (Red point)
-Observe that when bars L_2 and L_4 are in parallel positions, L_3 is perpendicular for both bars