an objective lens for focusing the electron beam emitted from said electron source upon the object using {HEAD ~ an output} from {TAIL ~ the height detector} 
from
an objective lens for focusing the electron beam emitted from said electron source upon the object using { HEAD ~ an output } from { TAIL ~ the height detector }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL