If an error has been made, it is better to cross it out and make a new entry. While records in pencil are better than no records, it is best to have them in permanent medium, such as ink or indelible pencil. Entries should never be changed or enlarged at a later date, unless the nature of the change is clearly indicated and dated by itself. Here again, it is better to make a new entry, pointing out the change. Pencil diagrams or sketches should never be retraced in ink.
Photographs are useful in keeping a complete laboratory notebook.
Particularly where a model has been made and successfully tested, it is desirable to take one or more photographs which will serve as a future indentification. The photographs can be permanently pasted into the laboratory notebook, with date and identification, and the name of the photographer. Laboratory books should never be mutilated, as by tearing or cutting out pages. When a project is divided between two or more investigators or groups, at least one group should make occasional entries showing the relation of the groups to the project as a whole, and indicating how a compound or equipment being developed by the different groups is to be combined in a common system. In interference proceedings, the Patent Office has ruled that an inventor is not competent to prove the making and reduction to practice of an invention by his own testimony.