A hard-bound book is the best, but a spiral-bound notebook will work as long as the pages are numbered and kept intact. The inventor's logbook can cover many ideas as long as they are all witnessed. You should keep separate logbooks or project books on any major invention that will generate a large amount of data or drawings in the development of the idea.
Looseleaf notebooks sometimes do not work as well as hardbound books, because pages can be added and deleted at will. This could become a bone of contention with attorneys if your logbooks are ever required as evidence in a court of law. This is the reason for the development of the BIDS (Basic Idea Development Sheet) system of documentation. The BIDS system allows the use of looseleaf sheets to successfully coordinate a project's development. These sheets are set up to be individually dated and witnessed. They can be arranged in a looseleaf notebook with other forms to form a comprehensive documentation package on an invention's development.
