The determination of the distribution of the unseen hands and the location of the missing high cards by logical deduction from the bidding and play.
Suppose you are playing in a spade contract after East has bid diamonds and West has supported. West leads the ♦2 and East plays the ♦K. From the bidding and the size of the spot card led, you place West with four diamonds and East with five.
You can also place the picture cards in the suit. West must have the ♦Q (or East would have played the card, the lower of touching honours in third seat, rather than the ♦K) and East surely holds the ♦J (or West would have led the ♦Q rather than fourth best). West therefore started with Q-x-x-x and East with K-J-x-x-x. The information that East has 4 points in diamonds to West’s 2 may then help you to place cards in another suit.
