G D P Is the Economy's Receipt

You are standing at the counter of a neighborhood burrito place at twelve fifteen on a Thursday. The lunch line is moving. Someone in front of you adds guacamole. The cashier taps the screen, the receipt prints, and the shop owner smiles because every table is full. That little receipt is more than lunch. It is a tiny clue about one of the biggest numbers in the economy: G D P, gross domestic product.