Explore the range of human hearing. Move the slider to sweep a pure tone from 20 Hz to 20 kHz, or let it sweep automatically, and note where the tone becomes hard to hear. Then try the listening game, which tests how small a frequency difference you can detect. Use headphones at a comfortable level.
This is not a medical hearing test. What you hear depends heavily on your headphones or loudspeakers, the volume setting, and background noise.
What to notice: sensitivity is not flat across frequencies, and near 1000 Hz most listeners can detect differences well below one percent.