If a team trades an extended rookie between the date his extension is signed and the date it takes effect, his "trade value" for the receiving team is the average of the salaries in the last year of the scale contract and each year of the extension. This is called the poison pill provision. The sending team uses the player's actual salary when calculating their outgoing salary. They use the current-year maximum salary in place of the (unknown) maximum salary for a future season, if necessary.
Here is an example of a poison pill calculation: Carmelo Anthony earns $4,694,041 in 2006-07, the final year of his rookie scale contract. Prior to October 31, 2006 he signed a five year extension (bringing the total seasons to six) for the maximum salary, with the maximum 10.5% raises. Anthony's actual salary will not be determined until July 2007, when the maximum salary amounts for 2007-08 are set. During the 2006-07 season the 2006-07 maximum is assumed for the 2007-08 season ($13,762,775), and the salary in subsequent seasons is based on this amount ($15,070,550, $16,378,325 and $17,686,100, respectively). If Anthony is traded during the 2006-07 season, then his outgoing salary from the Nuggets' perspective is his actual salary of $4,694,041. His incoming salary from the other team's perspective would be $13,518,358 -- the average of his 2006-07 salary and the assumed salaries in the extension.