Osmotic pressure and vapor pressure methods are used to determine absolute values of Mn, while light scattering and sedimentation velocity are used to determine Mw. However, if the GPC equipment is coupled with different detection techniques, such as light scattering, viscometry, refractive index, etc., then it is possible to obtain absolute MWs of polymers. Table 17.1 shows the different techniques used to measure different average MWs of polymers. It can be appreciated that GPC measures all MW averages. The different average MWs obtained by GPC can be represented in a MWD curve, as appreciated in Figure 17.2.