Abstract: A mobile telephony handset has a wireless communications transceiver for exchanging signals with a base station, and a positioning receiver for receiving coded ranging signals from a satellite-based positioning system. The handset is configured such that the positioning receiver is activated only periodically to perform a position fix using the ranging signals and between such active periods is in a power-saving condition. Each position fix includes a respective time measurement in which a precision time indication referenced to the positioning system reference time source is recorded and saved. The handset includes calibration means, which generates a calibrated time reference for performing each of a plurality of new such position fixes.