{HEAD ~ A stair cleaning device} 6 wherein {TAIL ~ the area} swept by the cleaning heads on rotation of the disc is a circle having a diameter of about 200 mm 
wherein
{ HEAD ~ A stair cleaning device } 6 wherein { TAIL ~ the area } swept by the cleaning heads on rotation of the disc is a circle having a diameter of about 200 mm
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH