If you've ever been in desperate need for a ruler and at the same time had the desire to slide your iPhone against some random surface, then RulerPlus is the app for you. This app offers you the ability to measure out a whole 7 centimeters or 2 inches on a single screen. Plus you can easily extend that out to as high as 98 centimeters or inches!
On each side you can actually increase it by another length of that measuring surface so you don't have to add in your head how many times you've moved over the two inch mark on your iPhone. There's also a clear button for you to start everything over from scratch. Besides that, there really isn't any other functionality that this app has to offer.
The worry with using this app is that the screen is so far away from the sides. If you decided to put a case on it, the it's even further away, making it less useful. If you were measuring something that you could place on to of it. perhaps it wouldn't be so bad, but some of those iPhones cost people $600. These screens may be pretty strong, but would you really want to use it as a measuring surface for anything?
If someone wanted to know the size of a business card, then this app would be perfect. But until the iPhone is indestructible or completely scratch resistant, having a ruler app for your iPhone is pretty limited in what it can actually do.