This specialized slide rule calculates load tolerances for modern-day military aircraft. We designed it in collaboration with Grace, a military contractor, who wanted an updated version of a slide rule already in use. Because the device must function in a wide variety of unforgiving climates, we developed the new version using PVC II. This ultra-durable material is both chemical and impact-resistant; and withstands temperatures from -40 degrees to +140 degrees Fahrenheit. It’s also much thicker than plastic or paperboard, so it stands up to rough handling and excessive wind shear for years of dependable service.