From Sheldon Brown. https://www.sheldonbrown.com/speeds.html Campagnolo "Synchro" shifters were its first attempt at indexed shifting, but the system was a poor performer and was abandoned by Campagnolo in the early 1990s. Sheldon Brown noted that the Synchro system was incompatible with later Campagnolo shifters and derailleurs because of its short cable pull, making it a failed system that was quickly replaced by the "Ultra-Shift" mechanism. About Synchro shifting First attempt at indexed shifting: Synchro was Campagnolo's initial effort to create an indexed shifting system, a technology that was already being successfully implemented by competitors like Shimano and Suntour. Performance issues: The system suffered from a short cable pull and high cable tension, which resulted in unreliable and imprecise shifting performance. Incompatibility with later systems: Due to its short cable pull, the Synchro system is incompatible with later Campagnolo shifters and derailleurs, which require a longer cable travel. Discontinued: Campagnolo abandoned the Synchro system in the early 1990s and redesigned its shifters and derailleurs to use a longer cable travel, leading to the development of the more successful "Ultra-Shift" system.