Colorimetric testers are devices used to measure the concentration of a substance in a solution by analyzing its color. They work on the principle that different concentrations of a substance will produce different colors when mixed with a reagent. By comparing the color of the solution to a standard color chart, users can determine the concentration of the target substance. These testers are commonly used in various fields, including water quality testing, food safety, and environmental monitoring. They provide a simple and quick way to obtain results without the need for complex laboratory equipment, making them accessible for both professionals and hobbyists.