A satellite positioning receiver comprising: an RF front end, for receiving satellite positioning signals; an analogue-to-digital converter, for sampling the received signals to generate signal samples; a memory; and a processor, for processing the signal samples to derive ranging measurements and to calculate a position fix, the receiver having a first mode in which the processor is operable: to process a first set of the samples as they are generated, to calculate a first position fix; to store in the memory information associated with this calculation; to process a third set of the samples as they are generated, to calculate a third position fix; and to store in the memory information associated with this calculation, the receiver having a second mode in which it is operable to store a second set of the samples, or ranging measurements derived from the second set of samples, in the memory for later processing to calculate a second position fix, the receiver having a third mode in which the processor is operable: to retrieve the stored second set of samples or ranging measurements from the memory; and to process them to calculate the second position fix, wherein said processing is assisted by the information associated with the calculation of the first position fix and the information associated with the calculation of the third position fix. an RF front end, for receiving satellite positioning signals; an analogue-to-digital converter, for sampling the received signals to generate signal samples; a memory; and a processor, for processing the signal samples to derive ranging measurements and to calculate a position fix, the receiver having a first mode in which the processor is operable: to process a first set of the samples as they are generated, to calculate a first position fix; to store in the memory information associated with this calculation; to process a third set of the samples as they are generated, to calculate a third position fix; and to store in the memory information associated with this calculation, to process a first set of the samples as they are generated, to calculate a first position fix; to store in the memory information associated with this calculation; to process a third set of the samples as they are generated, to calculate a third position fix; and to store in the memory information associated with this calculation, the receiver having a second mode in which it is operable to store a second set of the samples, or ranging measurements derived from the second set of samples, in the memory for later processing to calculate a second position fix, the receiver having a third mode in which the processor is operable: to retrieve the stored second set of samples or ranging measurements from the memory; and to process them to calculate the second position fix, wherein said processing is assisted by the information associated with the calculation of the first position fix and the information associated with the calculation of the third position fix. to retrieve the stored second set of samples or ranging measurements from the memory; and to process them to calculate the second position fix, wherein said processing is assisted by the information associated with the calculation of the first position fix and the information associated with the calculation of the third position fix.