A robotic work tool system, comprising a robotic work tool, said robotic work tool comprising a position determining device for determining a current position and at least one deduced reckoning (also known as dead reckoning) navigation sensor, the robotic work tool being configured to determine that a reliable and accurate current position is possible to determine and in response thereto determine an expected navigation parameter, compare the expected navigation parameter to a current navigation parameter to determine a navigation error, determine if the navigation error is negligible, and if the navigation error is not negligible, cause the robotic work tool to change its trajectory to accommodate for the navigation error.To be published with figure 5.
