Tsis siv neeg cov duab kos yog siv los ntsuas qhov ntev ntawm cov khoom lag luam thiab cov pwm. Qhov ntsuas ntsuas ntawm tsis siv neeg impermer muaj xws li cov ntsiab lus tsis raug, concentricity, ncaj, Contour qhov raug, kev sib ncig, thiab qhov loj me muaj feem xyuam rau cov qauv