A navigation device includes accelerometers for measuring movement. Given a beginning location and orientation, the device determines current location and orientation based on the information from the accelerometers. A user enters a list of items, such as a shopping list, into the device and the device determines a path to the items. The device then generates and presents directions for navigation. The path may be calculated to avoid hazards; such as shelves being stocked, congested checkout lines, and spilled items. The item list may be loaded into the device, using the bar code reader, optical character recognition, or through a store computer or the Internet. Planes of infrared beams are arranged within the environment such that a navigation device is likely to or must pass through a plane. A path may be computed to ensure that the navigation device passes through an IR plane. The navigation device has a plurality of IR sensors arranged in a tetrahedron. As the device passes through an IR plane, the device receives signals from the sensors. Given the order and timing of the signals and a location of the IR plane, the device performs a calibration. The device is calibrated without requiring the user to place the device in a cradle.