From the Store description:
Want to measure something in real life? Got your awesome Windows Phone?
Got a card from you wallet? You now have a Magic Ruler!
FEATURES
- FREE (supported by Ads)
- Measure anything
- One tap focus
- Units available: centimeters (cm), millimeters (mm), inches (in)
- Settings allow you to update card specifications
- Secure and safe to use
HOW DOES IT WORK?
- The Magic Ruler intelligently uses a common card as a reference
Here's a walkthrough and assessment, I'm trying to measure the length of my Nokia Lumia 1020:
The interface is ultra simple, though it's easier to show you (below) the actual workings rather than you trying to work it out from the instructions above.
The only setting is if your country uses a non standard credit card size (unlikely). And by 'width' the app means 'length', which is a little confusing! (right) to get started, you tap on 'Measure' and then use the camera interface included to snap your chosen object next to any convenient card.
A 'virtual' card is then shown and can be shrunk and rotated (using the controls provided) until it exactly covers your physical card in the photo. (right) Simple maths/geometry then allows Magic Ruler to calculate the respective size of a real (physical) ruler and to provide that (virtually) in the photo. Again, rotate (with multi-touch) and drag as needed and then measure by eye.
In the example above, I'd put the Lumia 1020 at just under 13cm long. The specs say 13.0, which is quite an impressive result.
Of course, most of us have rulers around our houses and offices, but not so much as in the 'old' days - making a smartphone camera-based virtual ruler more useful than you might think.
Gimmick or life saver? Either way, Magic Ruler is a free download here in the Store.