even though this relationship is empirical and less precise than the surface tension of a homologous series of liquids, it is very useful considering it is a parameter of the solid surface. this method is especially used to compare and measure the critical surface tension of low-energy solids (mainly plastics) very quickly and easily. figure 4 in zisman's published article from 1964 shows the critical surface tension as a measure of wettability of polyethylene. zisman published this analysis in 1964 and used a variety of nonhomologous liquids to measure the critical surface tension of polyethylene to be around 35 dynes per centimeter as shown by the intercept at x=1 in figure 4. figure 12 in zisman's 1964 article shows that different solids can also be plotted on the same graph to easily compare the critical solid surface tensions of a variety of plastic substrates including very different polymers such as teflon, acid monolayers, and esters. the zisman plot proved to be a breakthrough which allowed for a very efficient way to measure wettability of a solid which helped to spawn the work of dann in the late 1960s. dann characterized the critical surface tensions of a variety of polymeric materials using the zisman plot. in modern days, david and neumann in an investigation of contact angle on low-energy surfaces. however, today some different variations of the zisman plot exist because the dependent variable is unitless being since it is cosine of the contact angle for the liquid.