A method and apparatus are disclosed for determining the position, or change in the position, of a mobile terminal. The terminal has a receiver for receiving the signals from one or more transmission sources at unknown positions and an independent positioning device able to find, when operative, the position of the mobile terminal. The method uses the independent positioning device to measure the position of the mobile terminal at one or more first locations. A respective first set of time or phase offset values of signals received from the transmission sources relative to each other or to a reference in the mobile terminal is measured in the mobile terminal, at each first location. A second set of time or phase offset values are measured in the mobile terminal at a second terminal location where the independent positioning device is not operative and a second set of time or phase offset values of the signals received from the transmission sources, relative to each other or to a reference in the mobile terminal is measured. The values and said first measured terminal position or positions are combined, to thereby calculate the position of the mobile terminal at the second location, or the change in position of the mobile terminal between a first location and the second location.