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