Written laboratory records provide evidence of the date of conception of the invention, provide proof of inventorship, and show that the inventors used diligence in developing an idea. Such documentation is often needed if a third party contest the validity of the patent.
Best practices include.
Keep a written record of all ideas and experiments in ink, keep all records in bound notebooks with all pages numbered permanently in ink, keep lab notebooks intact and free from mutilation, record all experiments contemporaneously with the performance of the actual events. If the notebook entry records the conception of an idea, both the inventor and witnesses should sign and date the notebook entry and indicate that the witness has read and understood what has been written.