▁alt itudes . ▁ ▁It ▁is ▁also ▁used ▁as ▁the ▁indicator ▁of ▁angles ▁when ▁doing ▁calculations ▁with ▁the ▁instrument . ▁ ▁The ▁sl iding ▁be ad ▁facil it ates ▁trig on ometric ▁calculations ▁with ▁the ▁instrument . ▁ ▁Trad itionally ▁the ▁line ▁from ▁the ▁beginning ▁of ▁the ▁arc ▁to ▁the ▁a pe x ▁is ▁called ▁“ J a ib s ” ▁and ▁the ▁line ▁from ▁the ▁end ▁of ▁the ▁arc ▁to ▁the ▁a pe x ▁is ▁called ▁“ J a ib ▁tam ams ”. ▁Both ▁ja ib s ▁and ▁ja ib ▁tam ams ▁are ▁divided ▁into ▁ 6 0 ▁equal ▁units ▁and ▁the ▁si xty ▁ ▁parallel ▁lines ▁to ▁the ▁ja ib s ▁are ▁called ▁sit he eni ys ▁or ” ▁si xt ys ▁“ ▁and ▁the ▁si xty ▁parallel ▁lines ▁to ▁the ▁ja ib ▁tam ams ▁are ▁“ ju yo ob ul ▁m ab so ot ah ”. ▁ ▁The ▁reason ▁for ▁si xty ▁divisions ▁along ▁the ▁Ja ib s ▁and ▁Ja ib ▁Tam ams ▁is ▁that ▁the ▁instrument ▁uses ▁the ▁Sex ages imal ▁number ▁system . ▁That ▁is ▁it ▁is ▁graduated ▁to ▁the ▁number ▁base ▁ 6 0 ▁and ▁not ▁to ▁the ▁base ▁ 1 0 ▁or ▁decimal ▁system ▁that ▁we ▁presently ▁use . ▁ ▁Time , ▁angular ▁measurement ▁and ▁ge ographical ▁coordinate ▁measurements ▁are ▁about ▁the ▁only ▁hold ▁o vers ▁from ▁the ▁S umer ian / B ab yl onian ▁number ▁system ▁that ▁are ▁still ▁in ▁current ▁use . ▁ ▁Like ▁the ▁arc , ▁the ▁Ja ib s ▁and ▁Ja