Texas Instruments TI-84 Calculator

The Texas Instruments TI-84 has been the required graphing calculator for high school and college math classes since 2004. A device with a 96-by-64 pixel monochrome screen still selling for $110 in 2025 when phones can graph equations for free is one of the strangest product stories in consumer electronics. The interface uses a physical keypad with labeled function buttons, and the learning curve is steep enough that students spend the first week just figuring out how to enter a fraction. Pressing a button labeled 'Y=' and seeing a graph appear creates a connection between input and output that touchscreen calculators lack. TI's hold on the education market is institutional rather than technological. Test proctors approve the TI-84 and apps on phones are banned, and that regulatory moat is the real product. I think the calculator is a case study in how standards outlast the technology they were designed for. Objectively worse than free alternatives, it still sells millions of units per year.