{TAIL ~ A controller}, consisting in part of {HEAD ~ a single panel} or a series of panels, is provided to selectively open and close the apertures in response to the orientation of the eraser as it contacts the chalkboard 
{ TAIL ~ A controller } , consisting in part of { HEAD ~ a single panel } or a series of panels , is provided to selectively open and close the apertures in response to the orientation of the eraser as it contacts the chalkboard
TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH