Reading UCI Engine output in Arena Chess

Question

So for the most part I understand what I am looking at, but i have two questions about the first piece of data. Here is an example that I am looking at.

Firstly, the first column has values 1/4, 1/8, 2/17, 3/17. I'm pretty sure the numerator of those fractions indicates the depth of the search, but I am confused about the second number, my only guess being that it is the search depth of all non-quiet positions? IDK

Secondly, When I see a depth of 3, i expect to see a move order of length 3, but in the 3/17 search I am given a 6 move long line of play. Is this due to non-quiet nodes? The captures in the line make me believe so.

Thanks, any help, insight, and resources are appreciated.

Answer 1

http://www.chessforums.org/general-chess-discussion/9079-chess-engine-output.html

It’s the “search depth.” It tells you how deep the search has gone. The value is in “ply” or half-moves. The first number gives you the “brute force” depth, the second is the depth to which certain critical lines have been investigated. For instance a display of “depth = 12/30” means that the program has looked at every continuation to a depth of 12 ply (six moves), while some promising or dangerous continuations are being examined up to a depth of 30 ply (15 moves).

Please note chess engine always report in "ply", half-move.