wherein each of {HEAD ~ the elements} of {TAIL ~ the stack} is configured to be used individually for measuring hydration level 
of
wherein each of { HEAD ~ the elements } of { TAIL ~ the stack } is configured to be used individually for measuring hydration level
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH