I have joined this forum in need of some help. I am poor at physics but not too bad at math. I am making a device to place in a car to act as a dead reckoning navigation system using a digital compass and a 3 axis accelerometer. I tried measuring the speed of the car using one plane (axis) but the results were inaccurate. I have been researching that i can use all three to get a 3 dimensional acceleration. Will this tell me how fast i am travelling no matter the orientation of the device? I am unsure of the physics behind the forumlar that i would need to use. Is anyone able to help? I have already made the hardware and can get readouts from the accelerometers but the readouts are in g's. I need the calculated speed to be in a useful unit such as m/s or MPH. I have been researching and trying different methods all day.