A method of determining {HEAD ~ the level} of a material surface in a confined space, from {TAIL ~ a position} above said surface, using an ultrasound transducer positioned above said surface, said method including the steps of: 
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A method of determining { HEAD ~ the level } of a material surface in a confined space , from { TAIL ~ a position } above said surface , using an ultrasound transducer positioned above said surface , said method including the steps of :
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH 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 OTH OTH OTH OTH OTH OTH OTH