Physicians must account for the effects of multiple impairments using a summary value. Sometimes, when dealing with multiple impairments in a single case, the evaluating physician may be confused about whether specific impairments are added or combined, particularly during the assessment of hand or limb injuries. Combining is accomplished by using the Combined Values Chart presented in the Appendix of each edition of the AMA Guides to the Evaluation of Permanent Impairment (AMA Guides). With a few exceptions, the general rule is that all impairments should be combined. The combining must occur at the same hierarchal level (eg, upper extremity impairment can be combined only with another upper extremity impairment from the same limb), and whole person impairment (WPI) can be combined only with another WPI impairment. In case of impairments from a different limb (either from both upper or lower limbs) even though they may be expressed at the same hierarchal limb (eg, upper extremity or lower extremity), they should be combined at the WPI level only after the individual limb is fully rated and the final impairment for that limb is expressed at the WPI level. Evaluators should remember that impairing factors (sensory, motor, vascular, and so on) are combined at the smallest common unit (ie, digit < hand < upper extremity < whole person).