Alan Dye, Apple’s VP of human interface design, has discussed the Apple Watch UI in a new Monocle on Design podcast episode. It follows an interview on Hodinkee Radio earlier in the month.

He said that a core challenge with the user interface design was working with the smallest display ever seen in an Apple product …

Dye said that they went right back to basics when they first started working on the UI.

We spent a great deal of time thinking about […] how do we create a design system for Apple Watch that can live long into the future. A lot of what we were thinking about at the time were some core concepts around legibility – we’d certainly never worked with a display size that small; how do we impart a great deal of data on such a small screen at-a-glance?

It was in fact the need for small-screen legibility which led to the creation of what has now become Apple’s corporate font: San Francisco.

We spent a great deal of time looking back and learning about the history of time-keeping, to better understand how time has been kept through the ages, in more of a modern sense, and a lot of that guided the work we did on the watch faces.

Dye said that this same desire to maximize the amount of data that can be imparted at a glance made the decision to opt for a rectangular shape rather than a round one inevitable.

It forced us to create a new typeface which became eventually the typeface we use for all Apple products and all Apple marketing.

He also described the collaborative back-and-forth design process.

Dye also talks about the Apple Watch UI challenges as the number of features expanded – the battle between power and simplicity. This is also reflected in the growing number of watch faces. There are now more than 40 of these, and massively more variations via different complications.

We have this amazing process at Apple where we’re constantly collaborating across hardware, software engineering and of course the design studio. So it’s a constant conversation, and there’s a constant give-and-take, and so we’re asking for certain capabilities from a design perspective; we’re learning about new capabilities that come in from an engineering perspective; and ultimately that leads to the work that we end up doing.

You can download the podcast in Apple Podcasts.