Surveyor's Drafting Set Engineers used ruling pens, sectors and parallel rules to design and construct Valley Forge fortifications. Parallel Rule (top) Ivory or polished bone and brass. L 15.2, W 3.4 cm The George C. Neumann Collection, Valley Forge National Historical Park, VAFO 1816 Ruling Pen (middle) Metal, quill, L 9.3cm The George C. Neumann Collection, Valley Forge National Historical Park, VAFO 1811 Sector (bottom) Ivory and brass. L 15.8, W 3.3 cm The George C. Neumann Collection, Valley Forge National Historical Park, VAFO 1815