I can't find the page for rules about layering armor, and just a single sentence that only the highest armor a player is wearing applies... But Chummer doesn't seem to be doing that math properly, according to that sentence (p160, SR4a).
Here's what the player has, after buying Packs from the Runner's Kit, and adding it into Chummer:
Dermal Plate II (+2/2)
Form-fitting Body Armor (6/2)
Armor Vest (6/4)
Armor Jacket (8/6)
Chummer totals that up to 16/10, but that one sentence in the core book means it should be 10/8 (jacket being the highest armor rating, plus dermal plating's armor rating modifier). If I do just the Jacket and Vest, Chummer puts out the right number of 10/8. The Packs book, on p 22 (under multi-shooter) says that it provides (6/2) points of armor, not an armor ~bonus~.
Am I making this too complicated, or is that a misprint in the Packs booklet? I'm trying to make sure this guy is ready to go for our first real run tomorrow, by doing an audit at the GM's request. (I have SR experience from older editions, so... yea... audit duty. But I can't complain. It's helping me learn the new edition better than if I just read the sections I needed for my character.)