Apple iPhone 6s 3D Touch Is Surprisingly Complex

September 10, 2015 12:16 PM EDT

Apple blew through a lot of new products and features at its annual September event on Wednesday.

One of the most important is a new feature of the iPhone 6s and iPhone 6s Plus called 3D Touch, which will make the screens of the new devices pressure-sensitive, able to tell the difference between a tap and a hard press. The new functionality could change the way we navigate apps. When using an email app, for instance, a user could simply tap the subject line of a message to see the contents of the email, then let go to return to the inbox.

The feature seems simple, but such things rarely are in the world of consumer tech. In an in-depth profile on 3D Touch in Bloomberg Businessweek, Apple Senior Vice President of Software Engineering Craig Federighi explained how Apple’s new iPhones must be able to interpret screen presses that occur in all sorts of different contexts:

You’re trying to read minds. And yet you have a user who might be using his thumb, his finger, might be emotional at the moment, might be walking, might be laying on the couch. These things don’t affect intent, but they do affect what a sensor [inside the phone] sees. So there are a huge number of technical hurdles. We have to do sensor fusion with accelerometers to cancel out gravity—but when you turn [the device] a different way, we have to subtract out gravity. … Your thumb can read differently to the touch sensor than your finger would. That difference is important to understanding how to interpret the force. And so we’re fusing both what the force sensor is giving us with what the touch sensor is giving us about the nature of your interaction.

Basically, everything from how you’re holding your phone to whether you’re using your index finger or thumb plays a part in whether the iPhone will read a touch as a tap or a hard press. No wonder the company has spent “multi, multi, multi years” working on 3D Touch, in the words of Apple design guru Jony Ive.

Users will be able to try out 3D Touch for themselves when the iPhone 6s and 6s Plus launch on Sept. 25, starting at $199 with a two-year wireless contract.

Apple Exec Explains Why the New iPhone Has to ‘Read Minds’

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