In this work, a study, design and development process for an external linear sensor for one of Cranabs forestry machines has been carried out. The purpose of the degree project was to investigate and develop various design proposals for alternatives to linear sensors in crane extensions that are not built into a hydraulic cylinder.   The work began with a thorough literature study to research different types of sensors that would be suitable for the system. Through a series of brainstorming sessions, five concepts were generated, all dealing with different technologies: a rotary potentiometer, a laser distance sensor, a magnetic sensor, a belt and angle sensor, and a hall effect sensor.   Each concept was evaluated with respect to several different factors, including cost, installation difficulty, and measurement accuracy. This led to concept 3 (magnetic sensor) and concept 4 (belt and angle sensor) being chosen for further development. After a second iteration of these concepts, concept 4 was chosen as the final solution for further development due to its superior performance in terms of accuracy and cost.   In summary, this work has led to the development of simpler and more cost-effective linear sensor for crane extended and contributes valuable knowledge and information that can support further research and development in this area.