Original sentence: Sometimes, both arrow buttons appear next to each other for quick, precise manipulation without having to drag the thumb or move the mouse great distances to the other arrow; one of them may also be duplicated so as to show at both ends of the bar, providing familiarity for those used to both separate and adjacent buttons
Edited sentence: Sometimes, both arrow buttons appear next to each other for quick, precise manipulation without having to drag the thumb or move the mouse great distances to the other arrow (this was offered as an option in Mac OS 8.5); one of them may also be duplicated so as to show at both ends of the bar, providing familiarity for those used to both separate and adjacent buttons