The invention relates to a device for a length measurement providing a housing, a sending device for producing an optical measuring beam, a receiving device for detecting parts of the measuring beam that have beam scattered back from the measuring object and a redirecting device for redirecting the measuring beam that has been send out by the sending device and/or the receiving area of the receiving device. The invention relates also to an adapter for accommodating a device for a length measurement with a housing, a sending device for producing an optical measuring beam and a receiving device for detecting parts of the measuring beam that is scattered back from the measuring object, whereby the adapter provides frame for accommodating the device and a redirecting device for redirecting the measuring beam that has been send out by sending device and/or the receiving area of the receiving device.