Most of the ruler apps that we've seen for the iPhone put an image of a ruler directly onto your phone and have you use it as a ruler. While this works, it's not really taking advantage of what the iPhone has to offer. In fact, those apps aren't any better then just using an image of a ruler. RulerPhone is a much different sort of measuring app.
RulerPhone is easy to use and works very well. What you need to do is take a credit card sized object and place it up against what you want to measure. From there you take a picture, either through the app itself or pull it into the app from your photo album. Once it has read the image, all you have to do is line up a see-through blue card over the card in your photo and press ?lock card?.
By knowing the size of your credit card shaped object in the picture, you can now move a ruler anywhere around the image to get an actual measurement of the objects in your picture. The measurement is pretty accurate with most of the discrepancies coming from how well you line up the blue card to your actual card and if your ruler is right on the edge of the object you're measuring.
This is definitely the most creative and useful ruler app out for the iPhone. Considering it doesn't require you to slide your iPhone against a surface and uses more functionality then displaying an image. This app does cost a few dollars, but it is definitely worth it if you're looking for a measuring app. If you're not sure about RulerPhone, try out the lite version first, which is limited to a max ruler of 1.5 feet.