Over the past twenty years, accurate measurement of the seawater carbon dioxide system has become a high priority for scientists who have worked to understand just how much of the carbon dioxide created by man's activities has ended up in the ocean, where it is distributed, and how it has changed the chemistry of the oceans; a process known as ocean acidification. Andrew G. Dickson, Professor of Marine Chemistry at the Scripps Institution of Oceanography at UC San Diego, has been measuring carbon dioxide in seawater for over 30 years. In this two-part series, he introduces the basic chemical processes underlying the study of carbon dioxide in the oceans, and provides an overview of the experimental techniques that are in use to measure the levels of carbon dioxide in seawater indicating how a newcomer to this field might make decisions as to what research tools best suit them. (#23500)