▁to ▁sufficiently ▁hold ▁the ▁device ▁stable , ▁retain ing ▁the ▁optical ▁alignment , ▁with ▁just ▁one ▁hand . ▁ ▁M aking ▁alt itude ▁( e lev ation ) ▁measurements ▁of ▁the ▁Sun ▁being ▁simple ▁and ▁direct , ▁requiring ▁the ▁user ▁to ▁align ing ▁the ▁image ▁of ▁the ▁Sun ▁through ▁the ▁front ▁pin hole ▁( ap ert ure ), ▁centered ▁onto ▁the ▁rear ▁back ▁plate ▁which ▁oper ates ▁more ▁like ▁a ▁mask ▁and ▁not ▁a ▁view ing ▁pass ▁hole ▁for ▁sight ing ▁the ▁Sun ▁with ▁the ▁n aked ▁eye . ▁Much ▁in ▁the ▁same ▁manner ▁as ▁performing ▁e y ep ie ce ▁projection ▁with ▁a ▁teles cope , ▁one ▁fashion ed ▁with ▁a ▁front ▁and ▁rear ▁a pert ure ▁( font ▁l ens ▁and ▁rear ▁e y ep ie ce ) ▁along ▁with ▁a ▁projection ▁screen ▁behind ▁the ▁e y ep ie ce , ▁or ▁more ▁rud iment ary , ▁the ▁project ing ▁of ▁the ▁Sun ' s ▁image ▁upon ▁a ▁small ▁screen ▁plate ▁such ▁as ▁that ▁done ▁with ▁a ▁mar iner ' s ▁back ▁staff . ▁The ▁rear , ▁or ▁second ▁a pert ure ▁( pass ▁hole ) ▁having ▁the ▁function ▁of ▁working ▁as ▁a ▁black en ▁at ten u ator ▁so ▁that ▁any ▁reflect ing , ▁ann ulus ▁sh aped ▁sun light ▁off ▁the ▁metal ▁a pert ure ▁is ▁not ▁too ▁bright , ▁the ▁Sun ' s ▁image ▁( light ) ▁passing ▁through ▁the ▁second ▁hole ▁and ▁similar ▁in ▁task ▁though ▁void ▁of ▁a ▁fixed ▁image ▁plane , ▁to ▁that ▁of ▁an