How the Blind Spot Finder searches for what you missed

How it works

1. It works out how likely you are to reach each position

   Starting from move one, it carries a running chance down every line. Your own moves do not change that chance, because you always play your move. Only the opponent's choices divide it.

2. The likeliest positions are checked first

   Rather than grinding through the tree in order, it repeatedly picks the position you are most likely to actually reach and looks at that one next. The effort goes where the games are.

3. At each position it asks what opponents really play

   The database returns every reply from that position with the number of games behind it. That share becomes the chance of each reply.

4. A reply you cannot answer is a blind spot

   If you have a move saved against it, the scan simply continues down that line. If you do not, it is recorded as a gap, together with the chance of meeting it, which is how the results get ranked.

5. Lines too rare to matter are dropped

   Once a line falls below a one in ten thousand chance of occurring, it stops being followed. Without that cut-off the scan would spend forever on positions nobody will ever play against you.

6. Two move orders to the same position count once

   If your repertoire reaches the same position by more than one route, the chances are added together rather than counted twice, and everything below that position is rescaled to match.

What it will not do

• It needs a connection, because the comparison happens against a database rather than on your phone.
• It finds replies you have not covered. It does not judge the replies you have, so a covered line with a bad answer in it will pass the scan.
• Set the rating filter honestly. Scanning against master games will report gaps that nobody at your level is going to play.