Curious Ruler is a neat iPad app for measuring objects. The purpose of the app is to provide comparisons between common objects like coins (US, Canadian, and Euros) and the object that a student measures.
To use Curious Ruler students select an object from the menu of comparison objects. The list of comparison objects includes coins, basketballs, and iPads. Students then use the camera on their iPads to snap a picture of an object. For example I took a picture of my mouse and learned that an iPad was 2.5 times its size.
Curious Ruler isn’t the most robust app that you’ll find in the App Store and your students could do similar things with physical objects. That said, the use of Curious Ruler would be for students to check their answers after physically measuring and making comparisons.