In a nutshell

Nagra SN is a technological jewel mechanically and electronically. Milled from a solid piece of metal, hand-assembled according to Swiss watch making tradition, its miniaturization, which was extreme for the 70's, made it perfect for sound recording, even sync, in extreme conditions: high-risk documentaries, "embedded" on an actor (radio mikes did not exist at that time), sometimes on vehicles (stunts). It is even said that intelligence and police services used it. A whole range of accessories exists via a mini multipoint connector: 10 Hz quartz generator for sync shooting (SGXS), remote level control (SMR), condenser microphone (AKG CK) or lavalier condenser microphone (Nagrastatic), playback battery monitor (DSM) and all input and output cables. Unfortunately, because of age and short supply of media (1/8" tape) the Nagra SN is little by little being replaced by Apple Ipod and is hardly ever used in movies, except as an extra ...
Let's point out that Nagra still manufactures a stereo version of the SN for sound buffs.