Speed of Android device (user)

I need to know how fast the user with his Android device is moving. To do that I have started a periodic action with a Timer interval (ms) of 1000.

I think that if I compare / subtract two consecutive measurements, that I will then be able to calculate the user's speed.

2 Questions: 1) my Periodic Timer Name is fetchGPS. Where in the code can I "catch" that timer? and 2) How do I read the current position?

Thanks!

Stefaan