Androinica, a nice site for Android news and app information, has a nice article with Physics apps for Android that allow you to take measurements.
The apps include a ruler, distance measurement using your camera, protractor using gyro, sound meter, metal detector, compass, speedometer and Physics Gizmo from Phil Wagner (who's part of my PLN) which allows you to use the accelerometer for experiments.
These are some great ways to use Android devices in the classroom.
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