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