Which product design innovation is credited with making graphing calculators mainstream in mathematics education during the 1990s?

Throughout history, mathematical tools and products have evolved dramatically to meet the needs of students, professionals, and researchers. From ancient counting boards to modern computational devices, product design in mathematics has been driven by both technological advancement and user experience considerations. This trivia question explores how a major mathematical product design innovation changed an entire industry.

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Texas Instruments' introduction of the TI-83 with its user-friendly interface and programming capabilities
Casio's development of solar-powered scientific calculators eliminating the need for batteries
HP's reverse Polish notation system that eliminated the need for parentheses in complex calculations
Sharp's introduction of color LCD screens on their graphing calculator models