Keep written records of your progress in developing the invention:

(a) Write down all invention modifications, experiments, alternatives, and other details.
(b)  Keep copies of any emails, notes, letters, text messages or anything documenting discussions with others regarding your invention.

(c)   Keep receipts for anything that you buy for your invention, including parts, software, consultant costs, marketing costs, advertisements, or anything having to do with your invention.

(d)  Yes, these records must be in writing and dated.