It's a fantasy role-playing game.

DM: You are Grog Strongjaw, a goliath barbarian . You are the member of the famous group of adventurers. Previously, With you's hide- and leather-based armor having dissolved due to acid, Vax gives his magical armor to the goliath and instead dons his acid-resistant armor. Percy examines the cart.
DM: The armor you had on was hide, which was a dex bonus of 12 plus your dex. Studded leather is also the same, so your AC actually goes up.
Player: Oh! Ho! Something that you'd think!
DM: So, what was your AC previously?
Player: 18?
DM: 18?
Player: Yeah.
DM: It should now be 20.
