the fixed header 12 downward movement of the variable header track is limited by the vertical distance made available between the top of the variable header track and the bottom of the fixed header the variable header track must be fitted inside of the fixed header such that it cannot fall out of the fixed header with reference to fig1 a the design of a manually adjustable variable header track 14 according to the present invention incorporates a means for manually moving the variable header track upward and or downward inside the fixed header 12 such as adjustment screws 22 placed at regular intervals the manually adjustable variable header track works well to accommodate vertical movement of a corresponding building structure caused by static loads e g defection as a result of loads introduced after installation of the sliding unit when downward deflection occurs as illustrated in fig1 b such as when the corresponding building structure forces the fixed header 12 downward the variable header track 14 is manually adjusted upward inside the fixed header to provide the necessary clearance between the top of the sliding panel 18 and the variable header track such that the sliding panel moves freely when upward deflection occurs as illustrated in fig1 c.