After opening up the Soyuz navigation computer in [Part 1] and repairing damage from its apparently having been dropped (Soviet Soyuz ИНК Navigation Display, Part 1—Inside the Box), the next challenge for the restorers is reverse engineering the external interface, whose wires were brutally cut before the unit was received. Then it’s a matter of hooking up an external clock to drive it and see whether it works. In the process, more subtleties of orbital track prediction are discovered.