A method of calculating a position fix from satellite signal samples. The method comprises: obtaining first reference information produced during the calculation (120a) of a first position fix, the first position fix being the calculated position of a satellite-positioning receiver (5) at a first time; obtaining second reference information produced during the calculation (120b) of a second position fix, the second position fix being the calculated position of the receiver (5) at a second time; receiving a set of satellite signal samples generated by the receiver at a third time, or ranging measurements derived from such a set of satellite signal samples; and processing (140) the set of samples or the ranging measurements to calculate a third position fix. The processing (140) is assisted by the reference information produced during the calculation of the first and second position fixes.