I had never heard of these; could be a good lesson in a design class for thinking outside the box.
Reminds of that true? (probably not) story about NASA spending $50K USD to develop a pen that writes in zero gravity, while the Russians just use a pencil.
Reminds of that true? (probably not) story about NASA spending $50K USD to develop a pen that writes in zero gravity, while the Russians just use a pencil.