Peter Hatch wrote on Fri, Jul 18, 2003 02:24 PM EDT:Excellent ★★★★★
I've noticed that for the R1 through R7, the practical values seems to be
proportional to empty board mobility.
So if a Rook is worth 4.5 pawns, here are the calculated values and
Betza's comments on their actual value from the short rook and Wazir
pages:
R6 is 4.339 (worth a rook, most of the time)
R5 is 4.018 (a weak rook)
R4 is 3.536 (more than a bishop, but only slightly)
R3 is 2.893 (a bit weaker than a bishop, but close)
R2 is 2.089 (clearly less than a knight)
R1 is 1.125 (little more than a pawn)
My guess is that this is because a combination of practical concerns make
the endgame the prime determinant of a rook's value. Only one forward
direction, king interdiction, being stuck in a corner at the start, and
the bishop and knight not gaining power in the endgame as fast may all
contribute.
Or it could be something else entirely.