During use, as dust fills the bag, the bag expands and impinges upon a first of the pressure sensors and subsequently upon a second of the pressure sensors thereby indicating {HEAD ~ a filling} of {TAIL ~ the bag} with dust 
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During use , as dust fills the bag , the bag expands and impinges upon a first of the pressure sensors and subsequently upon a second of the pressure sensors thereby indicating { HEAD ~ a filling } of { TAIL ~ the bag } with dust
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH 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 OTH OTH