Doug was at the Reno November 1963 Graphics Conference and thought: "Oh, how would you control a cursor in different ways?" I remember how my head went back to a device called a planimeter that engineering uses."
Doug's notebook reads: "How about earlier idea of counting impulses from x+y displacement points? "..." Separate possibility of a 'bug' instead of a stylus. Bug being someting that does not fall if you take your hands off- just stay where you left it." This is significat as it contrasts with Licklider noted that the light pen should 'return to its resting place whenever the operator releases it".