Inside the computer, an electronic compass senses which direction the car is moving. By combining signals from the satellites and the compass with a reading from the speedometer, the computer's 32-bit microprocessor can accurately calculate the car location and bearing. It doesn't believe just one input. It's constantly recalibrating. A small color monitor displays a scrolling map, on which our car is represented as a moving blip.
Trouble soon materializes.
At the last intersection, right turns are prohibited between 9 a.m. and 6 p.m. The navigation unit can't foresee problems like that, but it can cope with them. We drive straight on instead, and the Voice immediately begins calling a new route. The instructions are surprisingly well timed, neither too early nor too late. As we barrel along a main road, we're even instructed to get into lane in preparation to turn left further on.