You are claiming to use a non computer to back up your computer!!!!Nobody claimed it was a computer. It is called a console for a reason. Any device that keeps a record of time & depth can be used as a backup. How did you ever learn to plan a dive using tables without a device that knows your depth and a device for dive time. Good thing I learned to dive before dive computers came along and made people lazy.
So you bring a dive table on every dive !!!!