So, I followed the instructions and got 7.7m as BD. I am assuming its inaccuracy. The way I calculated was take the length of DC in the side view (66mm) and divide that by 6.5, so 6.5/66 = 13/132. Then measure from D3 to B in the side view (78mm), the multiplied by the factor 13/132 and got 7.7m.