A simple camera could be positioned (perhaps attached to the head of the guitar) so as to view the hands moving over the fretboard. Perhaps visual methods which use commercial cameras to infer blood pressure could be used to estimate stress being applied by fingers [reference, reference]. Perhaps this would involve looking at changes in skin colour corresponding to blood flow restrictions resulting from stresses being applied. The apparatus described in this paper could be used to validate such an approach. Potentially the installation of a camera could potentially result in an apparatus more easily deployed at scale, and perhaps usable on many different instruments (without special fretboard modifications and such). Potentially it could also enable more dimensions of resolution, extending the one-dimensional limits of the described apparatus.

The term is Eulerian Video Magnification:

• https://www.youtube.com/watch?v=ONZcjs1Pjmk

Perhaps contemporary machine learning visual analysis could be applied also, and it would be potentially straightforward to record video data for training.

A more straightforward extension to the current study could be to apply visual analysis such that merely finger placements and gestures were identified to supplement the stress measurements. Indeed, visual analysis or motion capture approaches could be applied to video of the whole posture of the player for assessment of relationships between stress measurements across the fretboard and posture (such as sitting and standing), which can be significant.

Another complimentary measurement is audio. Stress/force sensor data could be supplemented with audio data analysis such as is employed by the likes of Yousician. A mentioned limitation of the apparatus is the measurement of vibrato effects/techniques. Could audio analysis supplement the existing apparatus's measuring capabilities to include such effects/techniques? Audio analysis can infer keys being typed on a keyboard, could it not also be used to infer frets being played, and with different forces applied?

Another form of sensor which may not have been considered is the Fiber Bragg Grating (FBG). Could this be feasible, perhaps in a specially-constructed fretboard? Would it add a greater resolution? Would it add a greater dimensionality to the stress measurements?

The characteristics of silicon strain gauges in terms of drift and hysteresis effects are well-understood and can be accounted for. Velostat foil can be used, but is perhaps more suited to cheaper, simpler applications like switches. The resistive sensors are dependent on temperature, but so are the light sensors used in the apparatus described.

Capacitive sensors are well-understood and potentially very cheap to make, e.g. they can be made from printed inks, beyond the more usual contemporary approach of Indium Tin Oxide (ITO). However, could the electrical fields of the strings be an issue? Although perhaps this could be understood using the Projected Capacitance Touch (PCT) approach with mutual capacitive sensors (for multi-touch sensors).

2 x ~$7,000

Apparently the smallest commercially-available 6-axis transducer, suited to robotic arms.

Couldn't this be higher? The TI MSP430 microcontroller family being used started in 1992. Still, it has good open source support.

Couldn't simple temperature sensors be added?

Use a non-breaking space.

Finite Element Analysis analysis

DC Comics, Detective Comics Comics

a fixed boundary condition against which the string can vibrate

What skill!

Style: For SI and NIST consistency, there should be a space between the numerical value and the unit symbol, here and in other cases in this document.

Could a clear definition of "correct" for this context be added?

Could more objective measurements of health improvements etc. be added?

Why refer only to careers? Why not refer to all musical instrument usage? The priority should be wellbeing, not economic productivity.

Technically perhaps this could be referred to as impulse-sensing, as impulse is force by time.

hello world