NEW YORK: Apple released a WatchKit, documentation and guidelines for developers alongside the new iOS 8.2 SDK. The WatchKit page includes a Getting Started with WatchKit video outlining the new tools.
The resources also let registered developers download a new font (called “San Francisco” for Apple Watch development), along with PSD templates for designers to develop mock ups of their applications.
You need to be a registered developer to download the tools, but anyone can read the Apple Watch Human Interface Guidelines, which outline the basics for designing for the Apple Watch.
It’s notable that the two different sizes of the Apple Watch (38mm and 42mm) have different resolutions, which results in different pixel sizes for on-screen elements and typography. Just as developers need to design for the different resolutions of the iPhone 4S, iPhone 5, iPhone 6 and iPhone 6 Plus, they also need to take the size differences of the two Apple Watch devices into account.
Apple says that developers can use the same image resources as long as it looks good on both screen sizes. If it doesn’t, developers will need to provide separate image resources for each one.