A mathematical calculation applicable when the original lead is construed as a fourth highest one. It is sometimes possible to obtain an exact reading of the distribution in all four hands.

The original rule as stated by R. F. Foster in 1890: "Subtract the pips on the card led from eleven; the result gives the number of cards higher than the one led in the other three hands". Counting such cards in his own hand and in the dummy, both the leader's partner and the declarer can determine the number of such cards in the concealed hand of the other.