1. **Problem Statement:** Find which diagram measures the median among the options: Bar diagram, Pie diagram, Dot diagram, and Box plot. 2. **Understanding the median:** The median is the middle value in a data set when the values are arranged in order. It is a measure of central tendency. 3. **Diagram types and their uses:** - Bar diagram: Used to represent frequency or count of categories. - Pie diagram: Shows proportions of parts to a whole. - Dot diagram: Displays individual data points. - Box plot: Summarizes data distribution including median, quartiles, and outliers. 4. **Key fact:** The box plot explicitly shows the median as a line inside the box. 5. **Conclusion:** The diagram that measures the median is the **Box plot**. **Final answer:** Box plot