A robotic lawnmower system comprising a robotic lawnmower arranged to execute a mowing pattern, said robotic lawnmower comprising a position determining device for determining a current position and at least one deduced reckoning navigation sensor , the robotic lawnmower being configured to navigate the robotic lawnmower based on the position determining device to execute the mowing pattern; determine that a reliable current position is not possible to determine based on the position determining device and in response thereto navigate the robotic lawnmower based on the at least one deduced reckoning navigation sensor ; determine that a reliable current position is again possible to determine and wherein the robotic lawnmower is further configured to, in response to determining that a reliable current position is again possible to determine: determine an expected navigation parameter; compare the expected navigation parameter to a current navigation parameter to determine a navigation error (Δ); determine if the navigation error (Δ) is detectable; and if the navigation error (Δ) is detectable, calibrate the at least one of the at least one deduced reckoning navigation sensor , wherein the navigation parameter is one or a combination taken from the group of navigation parameters comprising position and direction, and wherein the robotic lawnmower is configured to correct its current position and/or direction based on the navigation error (Δ), wherein the robotic lawnmower is configured to correct its position by steering towards an expected movement line. navigate the robotic lawnmower based on the position determining device to execute the mowing pattern; determine that a reliable current position is not possible to determine based on the position determining device and in response thereto navigate the robotic lawnmower based on the at least one deduced reckoning navigation sensor ; determine that a reliable current position is again possible to determine and wherein the robotic lawnmower is further configured to, in response to determining that a reliable current position is again possible to determine: determine an expected navigation parameter; compare the expected navigation parameter to a current navigation parameter to determine a navigation error (Δ); determine if the navigation error (Δ) is detectable; and if the navigation error (Δ) is detectable, calibrate the at least one of the at least one deduced reckoning navigation sensor , wherein the navigation parameter is one or a combination taken from the group of navigation parameters comprising position and direction, and wherein the robotic lawnmower is configured to correct its current position and/or direction based on the navigation error (Δ), wherein the robotic lawnmower is configured to correct its position by steering towards an expected movement line. determine an expected navigation parameter; compare the expected navigation parameter to a current navigation parameter to determine a navigation error (Δ); determine if the navigation error (Δ) is detectable; and if the navigation error (Δ) is detectable, calibrate the at least one of the at least one deduced reckoning navigation sensor , wherein the navigation parameter is one or a combination taken from the group of navigation parameters comprising position and direction, and wherein the robotic lawnmower is configured to correct its current position and/or direction based on the navigation error (Δ), wherein the robotic lawnmower is configured to correct its position by steering towards an expected movement line. <EOS>