Picture of Lego Mindstorms NXT Volume Calculator
This easy device will calculate the volume of any simple object. It's very easy to build, and lots of fun to use. If you like this, please vote. I could really use the prizes for my workshop. :)

Step 1: Building

Picture of Building
Add 4 black and 2 blue connectors to an L-bracket. (Pictured at bottom) Then insert one black connector into the middle of a 3-holed bracket. Connect the brackets as shown. Connect the cable from the motor to port C. The other nescessary additions are shown as notes on the picture.