The Handy Manual is a large book given to Lumi by Grandad which serve as your hint book throughout Lumino City. It contains diagrams and hints related to several of the puzzles. Its Table of Contents, in place of page numbers, lists math problems which you must solve.
Appearance[]
The manual contains over 900 pages. A note on the very first page from Grandad says "To Lumi, My work in progress. To be used in an emergency!" The table of contents show the page numbers of its corresponding puzzle, while the unmentioned pages in the book are just diagrams and descriptions of many more inventions.