The drawing is from the 1958 U.S. patent for a rocker-roller balance board designed by Frederic George Ludwig of Woodbridge, Connecticut. In the online database of the U.S. Patent and Trademark Office, the vers More
The drawing is from the 1958 U.S. patent for a rocker-roller balance board designed by Frederic George Ludwig of Woodbridge, Connecticut. In the online database of the U.S. Patent and Trademark Office, the vers More