Which innovative product design feature, introduced by Texas Instruments for their graphing calculators in the 1990s, revolutionized math education product marketing?

Mathematics textbooks and educational software have evolved dramatically in their marketing approaches over the decades. In the competitive field of mathematical educational products, companies have employed various strategies to distinguish their offerings from competitors. This poll tests your knowledge about a groundbreaking product design decision that revolutionized how mathematics textbooks were perceived and marketed to students and educators alike.

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The interchangeable colored faceplates that allowed personalization
The transparent casing that showed internal components
The glow-in-the-dark keypad for nighttime studying
The magnetic back that allowed attachment to whiteboards