That's cool but if you read back about 5 or 6 pages you will see the discussion of phone apps. and why they're not a solution for measuring slope in a moving vehicle.
What I have done/am doing is not difficult (despite 7 pages discussing it), I'm just messing about with it, rather than finishing it, and then only when I feel like doing so.
Edit: I suggested above prototyping on the shield or veroboard thinking I was the only one crazy/stupid enough to do it on cardboard instead but no, someone else has also done it:
http://lab.guilhermemartins.net/2009...rduino-prints/