What a position row shows
Each position in the database is stored as one row. The row keeps three things apart: what the engine said about this position itself, what the analysed moves below it add up to, and whether it is solved.
Scores are in centipawns (100 = one pawn) from the side to move, the chessdb.cn convention used everywhere on this site. Positions and the moves between them form a graph (see Repetition for why it is not a simple tree).
The fields
| Field | What it is |
|---|---|
eval_cp | The latest engine analysis of this position. It is what one search reported, and nothing more. |
backed_eval | The backed value: the best result the side to move can reach, worked out (by negamax) from the analyses that really exist below this position. |
backed_move | The move the backed value came through. It points at where to look; it is not a recommendation an engine made here. |
status, closure | For a solved position, the verdict and the gate it closed through. Anything still open carries UNKNOWN and no closure. |
backed_plies | How deep the backing chain runs, counted in plies (half-moves) below this position. |
backed_nodes | The analysis size of the weakest link on that chain. A long chain is worth what its thinnest search is worth. |
Which number a position shows
One position, one number. A position headlines its best known value, in this order:
- a proven status, if it has one;
- otherwise the backed value;
- otherwise the point eval (
eval_cp).
The point eval never headlines while something better is known. It stays available as the position's own search context in the tooltip and in the API point field.