This example combines a line chart and bar chart to explore groundwater levels at the Bog of the Ring, comparing two observation wells against effective rainfall. A brushed time-series chart filters the main visualization, updating a least-squares regression trendline and its equation. The main chart renders blue and orange lines for well measurements with a bar chart for rainfall, using d3.brushX, d3.nest, and d3.scaleTime. Data loads from CSV files, with SVG rendering and a categorical color legend.