AC on the 5E character sheet

AC seems to be a calculated field without the ability to manually set it. Where is it calculating the value from? I assumed the AC bonus of the armor that was in the equipment list, however,

I have a Hill Dwarf Fighter wearing Chainmail (AC 16, no dex mod) but the field is showing AC 18. Prof bonus shouldn't come into it and if I click the yellow star next to AC it doesn't change the value.

So my question is, why is my dwarf getting an extra 2 added to his AC? :)

[Edit] I was able to change it by editing 2 numbers in the character's XML file.

If you go to the combat tabe and click the searching glass icon next to the WND field, it will expand the calculations. If your referring to the hill dwarf entry fro mthe starter set pc, its because of his chain mail and shield.

Thanks. I did know that and forgot. No, I haven't got the Starter Set yet. Cheers