This is the middle tier of the position memory ladder. You see a chess position with 9 to 16 pieces for 60 seconds, the board goes blank, and you rebuild it from memory square by square. It sits between the first recall drills (3 to 8 pieces) and the expert tier (near-full positions), so it is the point where raw square-by-square memory stops scaling and you have to start chunking.
The skill it builds is grouping: instead of memorizing sixteen separate pieces, you learn to store a castled king with its pawn shield as one unit, a pawn chain as one diagonal, and a piece cluster as a shape. Sixty seconds is deliberately tight, it forces you to encode the position by pattern rather than by brute force. This is the same chunking that lets strong players glance at a middlegame and recall it later, and it feeds directly into blindfold play. For the full method behind the ladder, read the blindfold chess guide.