# Chart rules - `matplotlib.use("Agg")` before any pyplot import, always. - `savefig` only, 10 by 6 inches at 120 dpi unless the data needs otherwise; state the deviation in `result.md`. - Cap plotted points at 500; aggregate or sample beyond that. - One PNG plus its source CSV per chart, same basename. - Grid at 0.3 alpha, tight layout, rotated x labels on bar charts. - Colorblind-safe default cycle; never encode the only distinction in red versus green. - Every chart gets a one-line caption in `result.md` stating what the reader should conclude, not just what the axes are.