The Elektor Forum will close. See also this link. From Friday March 1st it is no longer possible to log in to the forum. However, the content of the forum will remain visible until the end of March. As of April 1st the forum will definitely go off the air.
In figure 2 is shown that vref (1,23V) is connected on the K1 connector. This in turn connected to the K2 connector of the mainboard. But looking at figure 3 there is no connection. So it floats or is not used.