The AMA Guides to the Evaluation of Permanent Impairment (AMA Guides), Third Edition, exclusively used the Range of Motion (ROM) Model to rate motion of the spine. The fourth edition requires the additional use of an inclinometer and also indicates that the Injury Model is the primary method for evaluating the spine; the ROM Model can be used as the differentiator or tie breaker. The ROM and the Injury Models cannot be used interchangeably, and the final rating always should be based on the Injury Model, not the ROM Model. One of the goals of changing the evaluation method is to create a more reproducible rating system. Because the Injury Model uses only objective findings present at the time of examination or found in the record, it is more reproducible. A further difference between the Injury and ROM Models is that in the former the examining physician rates the results of the injury, not the results of the treatment. The AMA Guides also requires that the patient's condition be stable—ie, not likely to change for one year. In the spine, the results of the injury, not the treatment, are rated, and often this can be done within several days of the injury.