System for determining relative positions comprising an encoder having encoder elements, and a sensor unit having a first sensor and at least one second sensor. The sensor unit and the encoder are movable relative to one another and their position relative to one another is determinable by the system. The first sensor and second sensor have a sensor distance with respect to one another. The sensor furthermore has a component composed of a dimensionally stable and aging-resistant material having a coefficient of thermal expansion which, in terms of absolute value, is in a range of 0 to 5·10−6K−1. The sensor distance is determinable highly precisely by the component by virtue of the component serving for the positional fixing of the sensors or by virtue of the component having a scale with the aid of which the sensor distance can be measured.