When the eraser is moved across a chalkboard to create airborne chalk dust, the apertures are selectively opened by the controller, {HEAD ~ the suction device} urging the airborne chalk dust through the apertures, through {TAIL ~ the cavity}, and into the collection chamber assembly where it is filtered and stored 
When the eraser is moved across a chalkboard to create airborne chalk dust , the apertures are selectively opened by the controller , { HEAD ~ the suction device } urging the airborne chalk dust through the apertures , through { TAIL ~ the cavity } , and into the collection chamber assembly where it is filtered and stored
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL OTH OTH OTH OTH OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH