Question about Zombies and base creature (PF)

[Griffin]

Hi, I have a question regarding transforming a creature into a zombie, the creature transformed (an ancient green dragon) has a high score of Natural Armor, the Zombien entry on PF reads as follows:

Armor Class: Natural armor is based on the zombie's size:

I'm not sure how to understand that, should I add the bonus of the table to existing Natural Armor or replace it?

Thanks for your input

Also, as a second question that I just remembered, is there any way to raised the BAB of an undead? the normal for PF is 3/4 of his HD, is there any way to make it better?

[Fouredged Sword]

Armor Class
Natural armor bonus increases by a number based on the zombie’s size:

Add them together, don't replace one with the other.

Now, you should also look up the zombie dragon template. This changes the way the zombie transformation interacts with dragons. It is generally better.

Pathfinder FAIL! My answer was 3.5!

Though it looks like they copied the chart exactly from the SRD. It lacks the adding wording though, so it will replace.