To break the coded arrangement of the alphanumeric serial designation, Langer worked with banking experts, examining records of currency from the previous 20 years in order to replicate the correct order. No records were kept by Operation Andreas and the method of how the Germans identified the correct sequences is not known; the paper historian Peter Bower states that it is possible that techniques adapted from those used in cryptanalysis were used to break the sequences. The German engravers working on the engraving plates struggled to reproduce the vignette of Britannia, which they nicknamed "Bloody Britannia" because it was so difficult. After seven months the forgers finished what they thought was a perfect copy, although Kenworthy states that the figure's eyes are incorrect.