This is reminiscent of the way an analog strobe tuner works when sampling a live 6-string guitar, other than just using it for tuning each string before playing.
Each open string is tuned to a reference Natural note without touching the string or fretting the note. The tuner is set for the desired note and when the string is tuned close enough, a bold strobe can be seen in one of the concentric tracks, apparently rotating far slower than the speed of the inner motorized disk. Fine-tuning to the guitar string is made until the strobe is as stationary as possible, minimizing any drift either clockwise or counter-clockwise.
The different concentric tracks in the spinning disk represent the different octaves for that note. When upper or relative harmonics are detected they appear as discernable but much less bold strobe effects.
The tuner is visualizing only one selected Natural, Sharp, or Flat note at a time, as the music goes along you are only going to see the notes and harmonics that are close to that one selected note. And any strobes seen over the full range of octaves when normally playing various stings and frets can be momentary for relatively stacatto triggers, or have various faint features over more sustained decay periods.
For instance if you leave the tuner set for E Natural after tuning your E string, you will get the most hits wben you play in the key of E too.
An adequately tuned & intonated guitar is not fully expected to get very many hits playing in too many other keys than what the tuner is set for.
A very well tuned & intonated guitar will show an abundance of those hits that are absent from the same instrument when its tuning is merely adequate.
Seems like the person in question re-invented "NNLS chroma" or "Harmonic Pitch Class Profiles", which are often used for automatic chord transcription and related tasks.
If you haven't yet, be sure to check out the one on dialup modem links. Seriously. It's a wonderful walk-through of all those screeches from the 1990s:
Each open string is tuned to a reference Natural note without touching the string or fretting the note. The tuner is set for the desired note and when the string is tuned close enough, a bold strobe can be seen in one of the concentric tracks, apparently rotating far slower than the speed of the inner motorized disk. Fine-tuning to the guitar string is made until the strobe is as stationary as possible, minimizing any drift either clockwise or counter-clockwise.
The different concentric tracks in the spinning disk represent the different octaves for that note. When upper or relative harmonics are detected they appear as discernable but much less bold strobe effects.
The tuner is visualizing only one selected Natural, Sharp, or Flat note at a time, as the music goes along you are only going to see the notes and harmonics that are close to that one selected note. And any strobes seen over the full range of octaves when normally playing various stings and frets can be momentary for relatively stacatto triggers, or have various faint features over more sustained decay periods.
For instance if you leave the tuner set for E Natural after tuning your E string, you will get the most hits wben you play in the key of E too.
An adequately tuned & intonated guitar is not fully expected to get very many hits playing in too many other keys than what the tuner is set for.
A very well tuned & intonated guitar will show an abundance of those hits that are absent from the same instrument when its tuning is merely adequate.