Logarithmic Scale
Instead of a linear scale with equal distances between every frequency, sound is typically displayed on a logarithmic scale.
Logarithms were developed in the 17th century by Scottish mathematician John Napier, the inventor of base 10 logarithms and German mathematician Nicholas Mercator, the inventor of base e, also called natural logarithms.
A logarithmic scale is exponential, so instead of being evenly spaced, the numbers get closer together as they go from 1 to 10, and also from 10 to 100, 100 to 1000, and so on. These blocks are known as "decades", since they have 10 divisions.
The distance between all octaves is the same, for example the distance between 100 and 200 Hz is the same as the distance between 200 and 400 Hz, 400 and 800 Hz, 1 kHz and 2 kHz and even 10kHz and 20kHz. This works well as a display for sound, since, like a piano keyboard, each octave has equal representation.