▁manual ▁arithmetic ▁methods . ▁ ▁App earance ▁ ▁A ▁full ▁set ▁of ▁Gen aille – L uc as ▁r ul ers ▁consists ▁of ▁eleven ▁stri ps ▁of ▁wood ▁or ▁metal . ▁ ▁On ▁each ▁strip ▁is ▁printed ▁a ▁column ▁of ▁tri angles ▁and ▁a ▁column ▁of ▁numbers : ▁ ▁Mult ip lication ▁ ▁By ▁arr anging ▁these ▁r ul ers ▁in ▁the ▁proper ▁order , ▁the ▁user ▁can ▁solve ▁multiplication ▁problems . ▁ ▁Consider ▁multip lying ▁ 5 2 7 4 9 ▁by ▁ 4 . ▁ ▁Five ▁r ul ers , ▁one ▁for ▁each ▁digit ▁of ▁ 5 2 7 4 9 , ▁are ▁arranged ▁side - by - side , ▁next ▁to ▁the ▁" index " ▁r uler : ▁ ▁The ▁second ▁multip lic and ▁is ▁ 4 , ▁so ▁we ▁look ▁at ▁the ▁fourth ▁row : ▁ ▁We ▁start ▁from ▁the ▁top ▁number ▁in ▁the ▁last ▁column ▁of ▁the ▁selected ▁row : ▁ ▁The ▁grey ▁triangle ▁points ▁the ▁way ▁to ▁the ▁next ▁number : ▁ ▁We ▁follow ▁the ▁tri angles ▁from ▁right ▁to ▁left , ▁until ▁we ▁reach ▁the ▁first ▁column . ▁ ▁Then ▁we ▁simply ▁read ▁off ▁the ▁digits ▁that ▁we ▁visited . ▁ ▁The ▁product , ▁shown ▁in ▁red , ▁is ▁ 2 1 0 9 9 6 . ▁ ▁Division ▁So on ▁after ▁their ▁development ▁by ▁Gen aille , ▁the ▁r ul ers ▁were ▁adapted ▁to ▁a ▁set ▁of ▁ro ds ▁that ▁can ▁perform ▁division . ▁The ▁division ▁ro ds ▁are ▁aligned ▁similarly ▁to ▁the ▁multiplication ▁ro