In FIGS 1 to 3, the weighting means 22 and therefore the aperture 24 are positioned at {TAIL ~ each} of the corners of {HEAD ~ the casing} 
In FIGS 1 to 3 , the weighting means 22 and therefore the aperture 24 are positioned at { TAIL ~ each } of the corners of { HEAD ~ the casing }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD