measuring {HEAD ~ a force} acting on {TAIL ~ the support device}, the force comprising the sum of: 
acting on
measuring { HEAD ~ a force } acting on { TAIL ~ the support device } , the force comprising the sum of :
OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH