There should be an embedded video here. If not then try this link instead.
It's all the more impressive when you realise that the entire mechanism in the writer was designed and built by hand. None of this modern-day CAD or CNC milling - each cog would have been handcrafted. Oh, and it's even programmable (after a fashion) - different letters can be selected to be written. In some ways it's the pinnacle of clockwork automata.
The rest of the programme is equally intriguing - it shows both large automata (like the mechanical turk, known in computing circles for what it isn't) and pocket-sized clockwork with tiny mechanisms (like a small singing bird early on in the show). Interestingly it gives the turk as inspiration for something else entirely - the power loom. The programme doesn't follow that chain of events any further, which is a shame as the power loom eventually became the Jacquard loom and that with its punch-card programming was the inspiration for the early computers.