"Ruler Game" This app for .99 cents is a quick and easy way to teach your students how to read a ruler. It is based off of a website called "The Ruler Game" but it is optimized to touch screen. It will help students grow and learn about fractions and the basics of a ruler.
How it works: You start the game and there is a timer. The game will give you a measurement and you have to drag your finger over the ruler to the selected mesurment. It sounds quite simple but when playing the game it can be quite challenging.
http://www.rulergame.net