http://www.lmgtfy.com/?q=iphone+dead+reckoning&l=1 http://www.lmgtfy.com/?q=iphone+dead+reckoning&l=1 decent answer in the second comment of the first google r

http://www.lmgtfy.com/?q=iphone+dead+reckoning&l=1 http://www.lmgtfy.com/?q=iphone+dead+reckoning&l=1 decent answer in the second comment of the first google result. Basically: There are 6 degrees of freedom: 3 translational, 3 rotational. To do dead reckoning you don't have enough information. If you can get over that issue (fix the phone or something), then the main issue is gravity, if you misalign by 1 degree even after 30s you will be way off.