There are already a handful of iOS apps that can turn your iPhone into a tape measure (minus the tape) in a pinch, but Incipio's new Rugged AR Case promises a usable level of accuracy when it comes to measuring distances of up to 6m.
The secret is a removable triangular augmented reality marker on the back that works alongside an accompanying app and the iPhone's camera. It provides the app with a reliable visual reference, since the smaller it appears in frame, the farther it is away from the phone.
Carpenters requiring extreme accuracy will probably still want to stick with what's in their toolbelt, but for quick room measurements when re-arranging furniture (and a little extra protection for your phone) the case might actually be worth the $US40 price tag. [Incipio]