1. The Free Beginner's Guide: 3Dprintingindustry.com. https://3dprintingindustry.com/3d-printing-basics-free-beginners-guide#02-history.
2. Flynt J. A Detailed History of 3D Printing: 3Dinsider.com. http://3dinsider.com/3d-printing-history.
3. History of 3D Printing: It's Older than You Are;Goldberg,2014
4. The Official History of the RepRap Project,2016
5. Natural Machines. www.naturalmachines.com/press-kit/.