After it's finished and plays in a range you like, I found it's nice to pull out a tuner and mark out where the notes are. Being familiar with the guitar, I made marks resembling a fretboard on the side of the stick next to the mylar, the fretmark placement dictated by the tuner. Doing this makes it a bit easier to see where the notes are. Interestingly, due to the nature of the oscillator design, the fretmarks will get progressively closer as the notes go higher, very much like a real fretboard.
Taming the square
The output of this instrument is a raw square wave. If you want it less harsh, you can put a simple fixed lowpass filter on the output, just before the 10uF capacitor. The filter consists of two parts...one capacitor and one resistor. The resistor can be a value between 2k Ohm and 5k Ohms. The capacitor should be 1 or 2 uF. Or instead of a fixed resistor, use a potentiometer between 2k and 5k Ohms. Using the pot allows the filtering to be variable.