A method for allowing a position receiver to determine position solutions from positioning signals (803-1, 803-2, 803-3, 804-3) from a plurality of autonomous positioning networks (801, 802) within a positioning system, wherein: each autonomous positioning network (801, 802) is synchronised to a different timebase; each of said plurality of autonomous positioning networks (801, 802) comprises one or more positioning-unit devices (801-1, 801-2, 801-3, 802-1, 802-2, 802-3); and when the position receiver is situated near the boundary of first and second of said plurality of autonomous positioning networks (801, 802), said position receiver receives positioning signals (803-1, 803-2, 803-3) from one or more positioning-unit devices (801-1, 801-2, 801-3) within said first autonomous positioning network and positioning signals from one or more positioning-unit devices from said second autonomous positioning network, and calculates its own position using the received positioning signals (803-1, 803-2, 803-3, 804-3), characterised in that: at least one positioning-unit device within said first autonomous positioning network receives positioning signals from at least one positioning-unit device from said second autonomous positioning network, measures the timebase difference between said first and second autonomous positioning networks (801, 802) and subsequently calculates a timebase clock correction, and incorporates said timebase clock correction into its positioning signals for transmission; other positioning-unit devices (801-1, 801-2) within said first autonomous positioning network receive and relay said positioning signals incorporating said timebase clock correction; and said position receiver receives positioning signals (803-1, 803-2, 803-3) incorporating said timebase clock correction from any positioning-unit device (801-1, 801-2, 801-3) within said first autonomous positioning network and applies said timebase clock correction to positioning signals received from said one or more positioning-unit devices from said second autonomous positioning network; such that positioning signals (803-1, 803-2, 803-3, 804-3) received from positioning-unit devices (801-1, 801-2, 801-3, 802-3) from said first and second autonomous positioning networks (801, 802) that are synchronised to different timebases can be used for position solutions. each autonomous positioning network (801, 802) is synchronised to a different timebase; each of said plurality of autonomous positioning networks (801, 802) comprises one or more positioning-unit devices (801-1, 801-2, 801-3, 802-1, 802-2, 802-3); and when the position receiver is situated near the boundary of first and second of said plurality of autonomous positioning networks (801, 802), said position receiver receives positioning signals (803-1, 803-2, 803-3) from one or more positioning-unit devices (801-1, 801-2, 801-3) within said first autonomous positioning network and positioning signals from one or more positioning-unit devices from said second autonomous positioning network, and calculates its own position using the received positioning signals (803-1, 803-2, 803-3, 804-3), characterised in that: at least one positioning-unit device within said first autonomous positioning network receives positioning signals from at least one positioning-unit device from said second autonomous positioning network, measures the timebase difference between said first and second autonomous positioning networks (801, 802) and subsequently calculates a timebase clock correction, and incorporates said timebase clock correction into its positioning signals for transmission; other positioning-unit devices (801-1, 801-2) within said first autonomous positioning network receive and relay said positioning signals incorporating said timebase clock correction; and said position receiver receives positioning signals (803-1, 803-2, 803-3) incorporating said timebase clock correction from any positioning-unit device (801-1, 801-2, 801-3) within said first autonomous positioning network and applies said timebase clock correction to positioning signals received from said one or more positioning-unit devices from said second autonomous positioning network; at least one positioning-unit device within said first autonomous positioning network receives positioning signals from at least one positioning-unit device from said second autonomous positioning network, measures the timebase difference between said first and second autonomous positioning networks (801, 802) and subsequently calculates a timebase clock correction, and incorporates said timebase clock correction into its positioning signals for transmission; other positioning-unit devices (801-1, 801-2) within said first autonomous positioning network receive and relay said positioning signals incorporating said timebase clock correction; and said position receiver receives positioning signals (803-1, 803-2, 803-3) incorporating said timebase clock correction from any positioning-unit device (801-1, 801-2, 801-3) within said first autonomous positioning network and applies said timebase clock correction to positioning signals received from said one or more positioning-unit devices from said second autonomous positioning network; such that positioning signals (803-1, 803-2, 803-3, 804-3) received from positioning-unit devices (801-1, 801-2, 801-3, 802-3) from said first and second autonomous positioning networks (801, 802) that are synchronised to different timebases can be used for position solutions.