NOTE: You better get everything inside Home, after this event you cannot enter Home again… So be sure to get those Al Bhed Primers!
When you reach the covert base, you’ll see a war waged between Yevon and Al Bhed. You’ll get into a lot of battles with Guado Guardians, who are very annoying(and wussy might I add), all they do is cause status effects and use magic. Take them out first…and when you reach your first save point inside, go to the right and down the end(don’t enter any of the doors) pick up the Al Bhed Primer Vol.XIX, then head into the door. When you encounter the two Chimeras, attack with Magic Break. Personally, Auron was my best character, casting Haste on him makes battles so much easier since he’s easily the strongest of all my characters.
When you find the treasure chest it’s decoded in Al Bhed, and depending on how many primers you have collected will determine how you decipher it. It’s much like Wheel of Fortune, you don’t need all the primers throughout the game to decipher them. The passcode will differ everytime you play it. The first number is given, then add. The next number is a given number then subtract, and then multiply the given number by a certain number that is given, then add the last number with the given number. There’s also a code of some sort to the right part of the room with four choices. Depending on what you choose will determine what answer goes with which. The 3rd choice goes with Brother, then Bikanel Island, then Al Bhed…in that order, this will allow you to pick up a Skill Sphere.
Now return to the save point and take the door next to it. Continue on through(make sure to check for treasure chests around and under the stairway.