the lower rail of the window sash the slider 34 moves along the sill in a straight line from right to left as the window opens and the force applied at the pivot connection 38 to the link 39 is almost perfectly in line with the direction of translation throughout the movement of the window sash between fully open and closed positions forces perpendicular to the line of translation are nearly zero for all window positions as the slider 34 moves toward the left to move the window sash to the full open wash position a pull is exerted on the links 42 and 43 which in coaction with the link 26 which is pivoted to the fixed second shoe 27 the window is caused to move outwardly as the first shoe 20 moves from right to left if the window is to have a fully open egress position shown in broken line in fig3 rather than a fully open wash position the operation of first shoe 20 and second shoe 27 is changed the screw 28 is removed from a hole 50 in the second shoe 27 to free this shoe for movement along the guide track 22 this screw is then used to secure the first shoe 20 in fixed position by insertion in a hole 50 and threading into the planar part 29 of the guide track as shown in broken line in fig3 the screw being identified at 28 39 for the opening of the window to an egress position the slider 34 moves from the position shown in fig2 to the position shown in broken line in fig3 this movement has caused.