Our lameness experts can usually determine the site of pain causing lameness by physical examination of the horse. The site of pain can often be localized using a hoof tester, manipulative tests and joint or nerve blocks. Many times, however, the lameness is too subtle or involves more than one limb to trust subjective evaluation of the response to these tests. We have computerized devices that are able to accurately tell us which limb the horse is lame in, the degree of lameness and the response of the horse to various test used to localize the site of pain. One of these instruments is the Lameness Locator® which is an inertial sensing device that measures asymmetry of torso motion to objectively quantify the degree of lameness. Our experience with the lameness Locator allows us to pick up a subtle lameness during a prepurchase examination and allows us to accurately diagnose the site of pain during evaluation of a horse with a subtle or complicated lameness. We have found that many horses that appear to have an obvious lameness involving a particular limb actually have pain in another limb and that the obviously lame limb is merely compensating for pain in another limb.