Continuously measuring total organic carbon (TOC) is both expensive and difficult, and so a common alternative is to use UV254 as a surrogate measurement. Because every water source is different, a correlation needs to be determined for each site; this relationship can then be entered into the analyzer, and a continual surrogate TOC output can be produced. The quality of this correlation will depend upon the makeup of the TOC in the water; the higher the proportion of UV254 absorbing organics, the better the correlation will be. The opposite is also true, as non-absorbing organics will not be detected by the sensor. However, we typically find that the correlations in wastewater and municipal applications are very good.