Jack and Jill, a digital man and woman, can examine your proposed CAD designs and tell what they can see and reach, how comfortable they are working on it, when and why they are getting hurt, when they are getting tired, and other ergonomic tidbits that help firms design safer, more effective products. The basic Jack software comes from UGS Tecnomatix (ugs.com) and lets users position biomechanically accurate digital humans of various sizes in virtual environments, assign them tasks, and analyze their performance. InterSense Inc., Bedford, Mass. (intersense.com) says it improves on the original package with its motion-tracking interface. InterSense software gives the duo a larger vocabulary that lets them reveal more about your product. The information the new Jack and Jill generate is most useful in the design stage.