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New iPhones' 3D Touch a complicated effort that took 'multi, multi, multi' years, Apple says

One of the central features of the iPhone 6s and 6s Plus, 3D Touch, was long in development and an extremely difficult technologically to get right, according to an interview with key Apple executives published on Wednesday.

The project was underway for "multi, multi, multi years," chief design officer Jonathan Ive told Bloomberg Businessweek. The company's senior VP of worldwide marketing, Phil Schiller, commented that engineering the hardware to make a display with something like with 3D Touch is "unbelievably hard."

The exact origins of 3D Touch are forgotten, but designers were reportedly exploring the concept of creating "shortcuts" from one function to another on an iPhone, dictated by the amount of pressure someone used on a touch display. Apple's senior VP of software engineering, Craig Federighi, explained that it was only once the company found a design it liked that it began considering how hard engineering it would be.

Some of the hurdles included dealing with the circumstances under which a person might be using 3D Touch. The result is that the feature has been built to detect both fingers and thumbs, and use accelerometers to cancel out the effects of gravity whether a person is walking or laying down, or an iPhone is tilted at odd angles.

The new iPhones sport bendable glass developed through a partnership with Corning, and 96 sensors embedded in the LCD's backlight that register each flex as a function of distance. Small vibrations from Apple's Taptic Engine are used to confirm when a press is successful.

At the moment, the 6s and 6s Plus are the only devices with 3D Touch, an evolution of the Force Touch technology used in the Apple Watch and recent MacBooks. The phones are due to ship on Sept. 25, following a preorder campaign starting Sept. 12.