HI Kei. Dr. Wilson Lennard had a hand in both the calculator (he developed it) and the Rules of Thumb (he worked with me on them). As you may have noticed, the calculator is much more specific, and I believe it was originally intended mostly for DWC systems. The Rules of Thumb are intended to be guildelines that are much more high level for more of a casual gardener.
Hope that helps!
Its does Sylvia! Such an honor to have your reply!
I just got your book and I will read it like a bible and then compare with the results I got in the calculator.
Thank you for taking the time!
Have a nice day!