This is a detail of the neck of a guitar fretted for just intonation. In just intonation, intervals are related by whole-number ratios. Instead of evenly dividing the octave into twelve parts, for example, each note is determined by a ratio. These whole number ratios allow notes to resonate more with the harmonic series.

For the guitar, it means you end up with awesome necks like this. (What would it sound like if you tried to bend a note on this thing?)

(via ljguitar)