provided the six units captured at K4 are not of greater value
than the six white units which are recaptured. In the present
instance both sides lose a pawn, two Knights, two Rooks, and a
Bishop, and there is no material loss. This established, he can
embark on the advance of the KP without any fear.

Therefore: in any combination which includes a number of
exchanges on one square, all you have to do is to count the
number of attacking and defending units, and to compare their
relative values; the latter must never be forgotten. If Black
were to play KtxP in the following position, because the pawn at
K 5 is attacked three times, and only supported twice, it would
be an obvious miscalculation, for the value of the defending
pieces is smaller. [Footnote: It is difficult to compare the
relative value of the different pieces, as so much depends on the
peculiarities of each position, but, generally speaking, minor
pieces, Bishop and Knight, are reckoned as equal; the Rook as
equal to a minor piece and one or two pawns (to have a Rook
against a minor piece, is to be the "exchange" ahead). The Queen
is equal to two Rooks or three minor pieces.]

---------------------------------------
8 | | | | | #R | | #K | |
|---------------------------------------|
7 | | | #P | | #R | | #P | #P |
|---------------------------------------|
6 | | #P | |#Kt | | #P | | |
|---------------------------------------|
5 | | | | | | | | |
|---------------------------------------|