All the various Executary models had a foolproof backspace mechanism that simply backspaced the head a fixed amount on the worm gear each time the "review" lever was pulled. Unlike the mechanism in Dictabelt machines which was a far more complicated solenoid based mechanism, IBM's backspacing method was simple and foolproof - requiring no adjustment or service calls as the far more complicated Dictabelt machines often did. The downside of this reliable simplicity, is that to backspace, meant the typist had to stop typing and reach over to actuate the lever, and then re-acquire the initial hand position. In the Dictaphone system, the typist could merely tap the foot switch without having to re-position her hand.. That was a major plus and a feature that most secretaries were unwilling to give up. Had IBM listened to the secretaries, they would have made far more market penetration. But alas, IBM... after all being IBM, thought they "knew better" and failed to listen to their customers... Let's face it: the secretaries ruled the office. Woe be to any office manager or purchasing dept that failed to give them what they wanted.... (Today as then: that proved to be a Big Mistake.....)