▁a ▁reg ulator ▁of ▁the ▁desired ▁sharp ness , ▁since ▁it ▁is ▁not ▁always ▁desired ▁to ▁make ▁the ▁graph ite ▁core ▁need le - sharp . ▁ ▁Other ▁systems ▁▁ ▁Some ▁older ▁models ▁like ▁the ▁ 1 8 9 7 ▁German ▁Jup iter ▁ 1 ▁used ▁revers ible ▁rot ary ▁cut ter - dis ks ▁with ▁cutting ▁edges ▁radi ating ▁from ▁the ▁center ▁on ▁each ▁side . ▁These ▁were ▁high - end ▁models , ▁quite ▁large ▁and ▁expensive . ▁O thers ▁simply ▁used ▁ab ras ives ▁like ▁sand paper . ▁In ▁some ▁cases ▁an ▁ab ras ive ▁was ▁used ▁to ▁shape ▁the ▁graph ite ▁core , ▁while ▁the ▁wood ▁was ▁cut ▁some ▁other ▁way . ▁ ▁Electric ▁sh ar pen ers ▁The ▁oldest ▁surv iving ▁electric ▁p enc il ▁sharp ener ▁is ▁the ▁Boston ▁Pol ar ▁Club ▁p enc il ▁sharp ener , ▁introduced ▁around ▁ 1 9 3 6 . ▁Electric ▁p enc il ▁sh ar pen ers ▁work ▁on ▁the ▁same ▁principle ▁as ▁manual ▁ones , ▁but ▁one ▁or ▁more ▁flat - bl aded ▁or ▁cyl ind rical ▁cut ters ▁are ▁rot ated ▁by ▁an ▁electric ▁motor . ▁Some ▁electric ▁p enc il ▁sh ar pen ers ▁are ▁power ed ▁by ▁batter ies ▁rather ▁than ▁being ▁plug ged ▁into ▁a ▁building ' s ▁elect rical ▁system , ▁making ▁them ▁more ▁port able . ▁ ▁Auto - stop ▁electric ▁p enc il ▁sh ar pen ers ▁are ▁able ▁to ▁sense ▁when ▁the ▁tip ▁of ▁the ▁p enc il ▁is ▁long ▁enough ,