1. A method for determining the location of a device, comprising: (a) receiving an estimate of the location of the device, the estimate having been calculated using initial estimates of the position of a plurality of transmitters; (b) calculating a set of range estimates using a revised estimate of the position of the device and revised estimates of the positions of the transmitters; (c) deriving an intermediate position estimate for the device based on the set of measurements and the initial position estimates for the transmitters; (d) computing an update vector based in part on the intermediate and revised position estimates for the device; and (e) updating the revised position estimate for the device based on the update vector.