Define &quot;best&quot;. We&#x27;ve used a quarter million dollar one at my current company, and at a previous job we spent far, far more than that for military airframes.<p>Groves &quot;Principles of GNSS, Inertial, and Multisensor Navigation Systems&quot; contains a good description of the various technologies used and their accuracy limits for navigation.<p>Consumer grade MEMS are fine for airbags, the pedometer in your phone, but are not sufficient for intertial navigation, even when aided with other sources. At around the $2K-30K you get systems that can provide accurate navigation for up to 2 minutes or so. They are used in things like missiles.<p>Aviation grade IMUs need to meet SNU 84 standard, which requires a maximum horizontal position drift of 1.5km in the first hour of operation. These will run 100K and up. Marine grade (subs, rockets, ICBMs) run $1 million and up, and have a maximum drift of 1.8km per day.<p>None of them are good enough for autonomous cars w&#x2F;o sensor fusion.