A position-determining apparatus, such as a GPS receiver, determines the position of the mobile device based on the time of flight of a transmitted probe signal using a method in which sections of the received signal is classified into two or more categories and accumulated according to categories before being used to compute the correlations familiar in the context of a matched filter. Using the method of the present invention to compute the correlations, and optionally applying additional time-saving techniques described herein, a position determination is achieved using arithmetic operations that are significantly reduced from that required in prior art methods to compute the correlations. The reduced number of arithmetic operations can reduce significantly the power consumption required of a device carrying out a method of the present invention, and thereby realizing a significant advantage.