Side-by-side comparison illustration (not a live screenshot — a designed diagram rendered with the Tessallite help-page palette). Left panel titled "expression_as_written" shows three input rows (region=EMEA sales=100 margin=30, region=EMEA sales=200 margin=40, region=EMEA sales=700 margin=90), an arrow labelled "aggregate first" pointing to a box "SUM(margin)=160, SUM(sales)=1000", then a second arrow labelled "evaluate expression" pointing to a result card "gross_margin_pct = 16.0%". Right panel titled "per_row_then_aggregate" shows the same three input rows, arrows labelled "evaluate per row" pointing to three intermediate values (30.0%, 20.0%, 12.9%), then a "SUM" arrow pointing to a result card "gross_margin_pct = 62.9%". Below both panels a caption box reads "Same data, same expression, very different answers. Pick the mode that matches the business question." Dimensions: 1200x600px. Purpose: make the aggregation-mode distinction obvious to business users who will otherwise treat the modes as interchangeable.