Which point-of-sale technology innovation first revolutionized U.S. military exchanges (PX/BX) during the post-Vietnam War modernization period?

Military Post Exchanges (PX) and Base Exchanges (BX) have a fascinating history in military retail. These stores have evolved dramatically from simple supply points to sophisticated retail operations. This trivia question focuses on how modern point-of-sale systems transformed military retail operations during a critical period in military history. Test your knowledge about the intersection of military retail innovation and technological advancement!

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Barcode scanning systems (1974-1976)
Punch card inventory tracking (1969-1971)
Electronic cash registers with tape backup (1981-1983)
Magnetic stripe ID card payment systems (1978-1980)