With the bottom bracket / seat tube down I can pull the down tube length from the drawing. Carefully aligning the frame over the drawing with the help of a machinist square and v-blocks I can now scribe the lines where the down tube intersects the bottom bracket. Also note, only the lug is only attached to the head tube at this point.
With the frame aligned about the drawing I can scribe the lines where the bottom bracket and down tube intersect. Notch out the lines and the down tube length is done.
