My math education predated the widespread use of graphing calculators. I remember writing my own BASIC programs to graph simple functions, but that was in a summer school programming class during middle school, not part of my high school curriculum. I’m amazed these old calculators cost this much.

Bulky and black, with large, colorful push buttons and a low-resolution screen, TI graphing calculators resemble top-of-the-line design from the 1990s and are functionally the same as when Texas Instruments first launched the TI-84 Plus in 2004. Even the price has remained almost the same. When my mom bought my TI-83 Plus calculator for ninth-grade math class in 2006, it cost $90 at our local Staples. Today, that calculator sells for $105 at Office Depot.

I remember feeling a pang of guilt watching my working-class single mom hand over her debit card to the cashier. On the short drive home, I held the calculator in my lap, still in its blister pack. I was 14 years old, and this was the most valuable electronic device I ever owned. —Medium