Lenovo announced the new Yoga Book today, a different take on the tablet idea. The Yoga Book has tablet-standard features like a 10-inch touchscreen and thin design, but it also has a unique, permanently attached panel that can be used as both a keyboard and writing surface. Not only that, you can also put a pad of paper on top of the panel and write your notes with real ink, while having them captured digitally at the same time.

The company says it spent three years working on the Yoga Book — much longer than the normal nine months it takes to develop a product — and as a result, went through a number of design iterations and concepts. We got a chance to see a handful of the design prototypes before today's announcement and they show how the company finalized and refined the design over time. What's perhaps most remarkable about the concepts and the final product is how little actually changed from the original form factor: the final Yoga Book is as thin and light as the first mock up, and roughly the same height and width.

You can see the progression of Lenovo's concepts below, and be sure to check out our deep dive into the development of the Yoga Book, as well.

Read Next: Rewriting the tablet: How Lenovo brought a dream design to life Photos by Sean O'Kane.

Grid View The final version next to a stack of prototypes.

One of the first ideas Lenovo had was to use two color displays, but it quickly scrapped it because of weight and power concerns.

From the beginning, the Yoga Book closely resembled a book.

Another two-screened prototype from the early stages.

Lenovo also played around with various integrated case designs. This one featured a pen holder for the stylus.

Another design with an integrated case and more plastic feel than the final version.

Some of the early design concepts for the Yoga Book.

This is one of the first mock ups with the touch panel opposite the main display.

Lenovo spent a lot of time designing various hinges for the Yoga Book before settling on the final one. Most of the these are broken because they failed reliability tests.

A closer look at one of the unused hinge designs.

Another scrapped hinge.

The eventual hinge design resembles the hinge Lenovo uses on its Yoga laptops. It is comprised of 130 different parts.

The final version on top of a number of prototypes.



