The distance of {TAIL ~ each focus point} from the best fit surface is then calculated and the largest distance is compared to {HEAD ~ a predetermined value} 
The distance of { TAIL ~ each focus point } from the best fit surface is then calculated and the largest distance is compared to { HEAD ~ a predetermined value }
OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD