> Although precise accelerometers exist in devices such as mobile phones and laptops, they must be recalibrated frequently and can only be used to navigate for

> Although precise accelerometers exist in devices such as mobile phones and laptops, they must be recalibrated frequently and can only be used to navigate for up to a few hours at a time. This sounds like they're using dead reckoning, i.e. integrating the acceleration twice to get the displacement from a known starting position. Regular accelerometers are too noisy and have a large drift because of this. Noise get's amplified when integrated, so if you're integrating twice you'll need a really low noise source.