▁even ▁be ▁at ▁the ▁same ▁distance ▁from ▁it . ▁ ▁Therefore , ▁the ▁rate ▁at ▁which ▁the ▁material ▁is ▁depos ited ▁on ▁the ▁sensor ▁may ▁not ▁equal ▁the ▁rate ▁at ▁which ▁it ▁is ▁depos ited ▁on ▁the ▁sample . ▁ ▁The ▁ratio ▁of ▁the ▁two ▁rates ▁is ▁sometimes ▁called ▁the ▁" tool ing ▁factor ". ▁ ▁For ▁careful ▁work , ▁the ▁tool ing ▁factor ▁should ▁be ▁checked ▁by ▁meas uring ▁the ▁amount ▁of ▁material ▁depos ited ▁on ▁some ▁samples ▁after ▁the ▁fact ▁and ▁comparing ▁it ▁to ▁what ▁the ▁thick ness ▁monitor ▁measured . ▁ ▁F ize au ▁inter fer om eters ▁are ▁often ▁used ▁to ▁do ▁this . ▁ ▁Many ▁other ▁techniques ▁might ▁be ▁used , ▁depending ▁on ▁the ▁thick ness ▁and ▁characteristics ▁of ▁the ▁thin ▁film , ▁including ▁surface ▁profil ers , ▁elli ps ometry , ▁dual ▁polar isation ▁inter fer ometry ▁and ▁sc anning ▁electron ▁micro sc opy ▁of ▁cross - sections ▁of ▁the ▁sample . ▁ ▁Many ▁thick ness ▁mon itors ▁and ▁controllers ▁allow ▁tool ing ▁factors ▁to ▁be ▁entered ▁into ▁the ▁device ▁before ▁de position ▁begins . ▁ ▁The ▁correct ▁tool ing ▁factor ▁can ▁be ▁calculated ▁as ▁follows : ▁ ▁where ▁F i ▁is ▁the ▁initial ▁tool ing ▁factor , ▁Ti ▁is ▁the ▁film ▁thick ness ▁indicated ▁by ▁the ▁instrument , ▁and ▁T m ▁is ▁the ▁actual , ▁independently ▁measured ▁thick ness ▁of ▁the ▁depos ited ▁film . ▁If ▁no ▁tool ing ▁factor ▁has ▁been ▁pres et ▁or ▁used ▁before , ▁F i ▁equals ▁ 1 . ▁ ▁References