This bar chart visualizes the average grade improvement for students who used different AI tools, including Copilot, ChatGPT, and Gemini. It compares these tools by calculating the mean difference between grades before and after AI usage from the `students_ai_usage.csv` dataset. The chart is rendered as an SVG using d3.v7, with `scaleBand` and `scaleLinear` for axes, and `rollup` and `mean` for data aggregation. Bars are colored purple, and hovering changes the fill to orange.