AccelerationG

This app allows you to measure the time period and g from a smart pendulum.

The phone is mounted on a scale with a hole at the edge. The app counts the number of oscillations and time period and hence calculates g. Enter the number of oscillations you want, the length and then press start and make the setup oscillate. It will give you the g value after the oscillations.

Keep phone vertical and press measure to get accelerometer y value (should be g) for comparision.