Which retail technology innovation, first patented in 1951 but conceptualized earlier, used parallel lines of varying widths to revolutionize inventory tracking and checkout efficiency?

Retail has evolved dramatically throughout history, from ancient marketplaces to digital storefronts. Behind today's shopping experience lies a fascinating history of innovations that revolutionized how people browse, select, and purchase goods. This trivia question focuses on a pivotal technological advancement that transformed retail operations in the early 20th century and set the foundation for modern inventory management and checkout systems we now take for granted.

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The Universal Product Code (UPC) barcode system
The mechanical cash register with receipt printing capability
The pneumatic tube payment transfer system
The Hollerith punched card inventory system