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