▁number ▁of ▁rot ations ▁of ▁the ▁sh aft ▁gives ▁the ▁speed , ▁hence ▁the ▁term ▁" integr ating " ▁in ▁the ▁P IG A ▁ac ron ym . ▁A ▁further ▁level ▁of ▁integration ▁of ▁sh aft ▁rot ations ▁by ▁either ▁electronic ▁means ▁or ▁by ▁mechanical ▁means , ▁such ▁as ▁a ▁Ball - and - disk ▁integr ator , ▁can ▁record ▁the ▁disp lacement ▁or ▁distance ▁tra ve led , ▁this ▁latter ▁mechanical ▁method ▁being ▁used ▁by ▁early ▁guidance ▁systems ▁prior ▁to ▁the ▁avail ability ▁of ▁suitable ▁digital ▁computers . ▁ ▁In ▁most ▁implementations ▁of ▁the ▁P IG A ▁the ▁gy ros cope ▁itself ▁is ▁cant ile ver ed ▁on ▁the ▁end ▁of ▁the ▁p end ul um ▁arm ▁to ▁act ▁as ▁the ▁p end ul ous ▁mass ▁itself . ▁▁ ▁Up ▁to ▁three ▁such ▁instruments ▁may ▁be ▁required ▁for ▁each ▁dimension ▁of ▁an ▁IN S ▁with ▁the ▁three ▁acceler om eters ▁mounted ▁orth og on ally ▁generally ▁on ▁a ▁platform ▁stabil ized ▁gy ro scop ically ▁within ▁a ▁system ▁of ▁g imb als . ▁ ▁A ▁critical ▁requirement ▁for ▁accuracy ▁is ▁low ▁static ▁fr iction ▁( st iction ) ▁in ▁the ▁bear ings ▁of ▁the ▁p end ul um ; ▁this ▁is ▁achieved ▁by ▁various ▁means ▁r anging ▁from ▁double ▁ball ▁bearing ▁with ▁a ▁super im posed ▁oscill atory ▁motion ▁to ▁d ither ▁the ▁bearing ▁above ▁its ▁threshold ▁or ▁through ▁the ▁use ▁of ▁g ase ous ▁or ▁fluid ▁bear ings ▁or ▁by ▁the ▁alternative ▁method ▁of ▁floating ▁the ▁gy ros cope ▁in ▁a