The focus information of each solder ball is used to determine the distance to {TAIL ~ the tips} of {HEAD ~ each solder ball} 
The focus information of each solder ball is used to determine the distance to { TAIL ~ the tips } of { HEAD ~ each solder ball }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD