4MOST calibration system: design, assembly, and testing

The Calibration Unit for 4MOST is providing hundreds of highly stable sharp spectral features with high power and mimicking the sky over the focal plane. The heart of the system is a combination of a bright broadband lamp and a Fabry-Perot etalon that provides a regular comb of spectral lines. 120 integrating spheres are distributed in 4 Light sabre linear arrays. These Light sabres are attached to the telescope spider struts and provide unvignetted illumination to the telescope focal plane. We describe the final design, the alignment, and the results of the testing.