Ideal size for all your notes, lists, sketches, estimates and calculations. Stashes in a van, sits on a desk. Plus, you'll have a proper record of who, what, when and where. Save your notebook when full so you can always refer back if necessary. On bigger jobs, why not use a dedicated notebook just for that contract ? Or maybe treat your subbies to their own notebook ? At least that might mean one less excuse when it comes to them not turning up on site :-)