▁highly ▁resist ant ▁to ▁mechanical ▁dr ift , ▁with ▁dr ift ▁requirements ▁as ▁low ▁as ▁a ▁few ▁n m / min ute ▁while ▁being ▁able ▁to ▁move ▁several ▁ μ m / min ute , ▁with ▁re position ing ▁accuracy ▁on ▁the ▁order ▁of ▁nan om eters . ▁Ear lier ▁designs ▁of ▁T EM ▁accomplished ▁this ▁with ▁a ▁complex ▁set ▁of ▁mechanical ▁down ge aring ▁devices , ▁allowing ▁the ▁operator ▁to ▁fin ely ▁control ▁the ▁motion ▁of ▁the ▁stage ▁by ▁several ▁rot ating ▁ro ds . ▁Modern ▁devices ▁may ▁use ▁elect rical ▁stage ▁designs , ▁using ▁sc rew ▁g ear ing ▁in ▁concert ▁with ▁ste pper ▁mot ors , ▁providing ▁the ▁operator ▁with ▁a ▁computer - based ▁stage ▁input , ▁such ▁as ▁a ▁jo yst ick ▁or ▁track ball . ▁ ▁Two ▁main ▁designs ▁for ▁stages ▁in ▁a ▁T EM ▁exist , ▁the ▁side - entry ▁and ▁top ▁entry ▁version . ▁Each ▁design ▁must ▁accommod ate ▁the ▁matching ▁holder ▁to ▁allow ▁for ▁spec imen ▁insert ion ▁without ▁either ▁dam aging ▁del icate ▁T EM ▁opt ics ▁or ▁allowing ▁gas ▁into ▁T EM ▁systems ▁under ▁vac u um . ▁▁ ▁The ▁most ▁common ▁is ▁the ▁side ▁entry ▁holder , ▁where ▁the ▁spec imen ▁is ▁placed ▁near ▁the ▁tip ▁of ▁a ▁long ▁metal ▁( br ass ▁or ▁st ain less ▁steel ) ▁rod , ▁with ▁the ▁spec imen ▁placed ▁flat ▁in ▁a ▁small ▁bore . ▁Al ong ▁the ▁rod ▁are ▁several ▁polym er ▁vac u um ▁rings ▁to ▁allow ▁for ▁the ▁formation ▁of ▁a ▁vac