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Forgive me if this has been asked elsewhere, but I've both Googled and searched here at CSE and cannot find an answer.

When I'm using an Engine for analysis (in this case, Stockfish 15), I've noticed that both the "Depth" and "Current Node" values are often expressed as a fraction.

What do these fractions represent?

Below is an image showing an example of what I mean. Depth is highlighted in red, current node in green.

Stockfish showing a fraction for both "Depth" and "Current Node"

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The first window shows depth of the calculation. Here 35 is the depth in plies (half-moves) which the engine has calculated pretty thoroughly, and 75 plies is the depth of selective search (some variations have been calculated to the depth of 75 plies! Some variations are considered important by the engine. It calculates them much further than the standard depth.

The second window shows the current move the engine computes. It's move number 6 out of 39 possible moves in the current position. Specifically, it's King to g8 and possible variations after that.

The third window shows the overall number of positions the engine has calculated in millions: 1,746 millions or around 1.7 billion. When dealing with engines the number of positions is usually referred to as the number of nodes. One node is one position. One KN (kilonode) is one thousand positions. One MN (Meganode) is one millions positions.

It's Fritz/ChessBase program, right?

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    yep, I'm using Stockfish 15 with Chessbase. When I use it with Arena or any other program, however, I've always seen the fractions and wondered what they meant. Really appreciate the information! I don't normally see the selective search depth go so high, and not long after I posted the above screenshot it dropped from 75 to 56 (went from showing 35/75 to 36/58). Is that because it actually "dropped" the lines it had calculated to depth 75 from the hash table, and now the "longest" line it'd calculated was up to 56 plies? Jul 14, 2022 at 22:04
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    Yeah, it drops some lines of its selective search. For example, in winning positions, the program may show a mate, say, in 27 (moves = 54 plies), then it drops to mate in 19 (19 moves = 38 plies) when the programs finds a better solution. So, yes the selective (non-thorough) search fluctuates.
    – user32756
    Jul 14, 2022 at 22:16
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    Fritz/ChessBase program is vast. At first it might be difficult to find certain options and descriptions. Normally, most of things can be found in the Help. It's now online: help.chessbase.com/Fritz/16/Eng They offer search thru Contents, Index, and Search. The program needs some studying at first, I believe. It has tons of stuff. It's geared to pros. Yet, Fritz has many options for amateurs and beginners. I remember myself having trouble 20 years ago trying to find how to turn off engine thinking while I was thinking, making that old engine too hard to play against :-)
    – user32756
    Jul 14, 2022 at 22:47

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