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