Theobald begin with his enneagon element in Figure 67, together with dodecagonˇ¦s element in Figure 99. The relationship between the radius of each figure is 12sin30^o R²{12}=9sin40^o R²{9}, and the width of octagonˇ¦s strip element is 2sin45^o R{8}. He crossposed them as Figure 104. This results in a 14-piece dissection of dodecagon to enneagon shown in Figure 103.

Reference :  Geometric Dissections-Gavin Theobald