Unfortunately, the typo gremlins got into the last version of the BF Bulletin 004 “Guide to ‘Warm Edge’ for windows and facades”, and that of all things in the formulas for the calculation of Uw and Ucw. Immediately upon discovery the typos were corrected. As of now, the latest version (Modification index 4, March 2017) is available for free download on the BF websites. Or you can directly get to the pdf-files of the Bulletin in German language here, to the English version here, and to the French please click here.