No. The last page is your summery and quick referance for playing.
All the info is a repeat of what is in the rest of the rule book.
OBIS
It is the long count calander and it is were it says the last day of the 13th bouktou.
yes
there are 30 codex pages in the game and you will have to find them around the cities to find them on the map you have to go up to view points that you have located and sync if there are any codex pages are in range they will show up on the map and they are always have 4 guards posted around a open door (if you don't want to fight them use thieves, contessas or mercenaries to distract them while you loot the box inside)
The most obvious suggestion is the best here, pick it up and read it start to finish. It shouldn't take too long, as there is a lot of stuff you can skip upon first reading (Background, technical stats) which you will only need later. Then once you've done that you'll have a good idea as to how your army's codex is laid out, so you know where to look for information when you need it.
Just use your eagle vision, select a codex page and click on it. It will rotate 90 degrees. Do this to all of them until it forms a map.
If you're talking about in-game, you need to have every codex page and rotate them so that, while using Eagle Vision, they all line up correctly. This leads to the final memories of the game, meaning that nobody will react to what you've done until you've gotten to that point in the storyline. If you mean showing your friends, you need to complete the Codex wall in order to get The Vault and An Old Friend Returns Xbox 360 Achievements. On the PS3, I'm sure there are trophies available for that point of the game as well.
the last page in what?
progress the story and you will receive a codex page for Leonardo. you the get to try it out! but takes ages to aim
It's a map of the world. Start with the edges and work your way in incase you aren't familiar with it.
on the last page
The codex pages arrange to look like a world map (of Earth, not the game world) so you should be able to figure it out with a standard map. There are a lot of pictures, though.
By stating that the codex pages are already unlocked, I'm assuming you need to know how to use them on the codex wall in the Villa. Just interact with the codex wall and turn on your eagle vision to see a scrambled image. Use the button which corresponds to the rotation of each page to assemble a world map. You can do this with any amount of pages you've found, but all 30 pages must be done when the congregation of assassins meed in the codex room much later in the game before leaving for Rome and the final stage. Now, finding those codex pages... you will see them in the town on your map if you purchased a treasure map for it and the rest will be awarded to you after completing certain missions. Good luck. ShaqueNova.