a pre determined distance apart the guides 116 cause the milled or blended aggregate to be discharged in a windrow 120 of substantially constant width w if the width is a known constant the only variable that needs to be measured to determine cross sectional area of the windrow 120 is its height h accordingly a height measuring device 122 is provided for measuring the height h of the windrow 120 various height measuring devices 122 may be used fig3 through 6 show representative examples in the fig3 variant a u201c shoe u201d 124 substantially spans the breadth of the discharge opening 114 and levels the windrow 120 as it rides upon the windrow 120 the shoe 124 has a base 126 which inclines upwardly toward a front end 128 thereof a parallel bar linkage 130 mounts the shoe 124 to the main mill 38 or pug mill 40 although this is likely the most convenient mounting location this should not be interpreted restrictively for example a separate mounting bracket might be used extending from the transport structure 11 a height transponder 132 is mounted to the parallel bar linkage 130 to send an electronic signal to the central processing unit 112 in response to vertical movement of the shoe 124 which is indicative of windrow height a counterweight 134 may also be provided to reduce the downward force exerted by palo the shoe 124 fig4 through.