This article (continued from the previous issue) discusses and clarifies 21 key principles for using the AMA Guides to the Evaluation of Permanent Impairment, (AMA Guides), Fourth Edition. Tests of inconsistency are good but imperfect indicators of patients’ efforts, and if observations or test results are insufficient, the physician should explain the modified impairment assessment in writing. The AMA Guides includes rules for interpolating, measuring and rounding, and evaluating, and physicians should be familiar with them. In general, impairment percentages allow for pain that may accompany the impairing condition. If possible, the evaluator should remove a patient's protheses during evaluation. Physicians should consult the Combined Values Chart if the effects of treatment prevent adequate impairment management. A patient's decision to decline therapy for a permanent impairment should neither increase nor decrease the estimated impairment. The AMA strongly encourages use of the most recent of the AMA Guides. Impairment percentages derived according to AMA Guides criteria should not be used to make direct financial awards or direct estimates of disabilities. Combining, compared to adding, is a mathematical process to prevent estimating impairments greater than 100%, and the Combined Values Chart provides guidance for use. Divergent ratings should be matters of fact, not opinion.