How do you get 100 percent synchronization in assassins creed 2

I think you need to get altairs armor

From cloud180:

You also must complete each secondary memory. This includes the feathers and treasures. You must also get all of the statuettes in the villa. Easy to find and all are in the city. If you do not have the black edition or the DLC you cannot get 100%. There are also 3 templar locations and 1 extra assassin's tomb that are required. To get the extra assassin's tomb you must have a ubisoft account and go to the ubisoft store in the game menu and collect from there.