A 25 × 20 mm ESP32-C3 board with a 0.42-inch OLED glued to it. Two things make it worth a skill: **the panel is a 72 × 40 window inside a 128 × 64 controller and does not start at column 0**, and **the C3 has exactly one I2C controller, which the panel occupies**. Almost every failure on this board traces back to one of those two facts, and neither is visible from the code.
