From John Gruber’s review of the iPhones 6 (emphasis added):
My understanding, talking to people at the event last week, is that Apple’s industrial design team mocked up prototypes of every single size between 4.0 and 6.0 inches, in tenths-of-an-inch increments, and from those 20 sizes selected the two that best hit the sweet spots for “regular iPhone” and “ginormous iPhone”.
Two takeaways with regards to my post yesterday about healthy design processes:
It’s sweet spots — plural. It’s never been more obvious that Apple’s design team can produce two different products that are equally faithful interpretations of unchanging principles. Both the 6 and the 6 Plus are unmistakably iPhones.
Tenths-of-an-inch increments. Not even Apple waltzes through a problem confident in their first or second draft. Someone said: let’s make every fucking size between four and six inches and try them all, and the team followed along. That’s the only way they could know for sure which sizes work best.