About the indicator's placement algorithm - rvalla/CalAr GitHub Wiki
CalAr will show you the tunning error for each harmonic's frequency with a graphic indicator over the piano keyboard. Note that the indicator placement is discretized by the program's window size (in other words, the indicator only can move an integer number of pixels). The width of the keyboard is about 800 pixels and the difference between the first and last frequency its keys represent is near 7900Hz. The graphic indicator's placement algorithm shows a shift with respect to the key when the tunning error is greater than 1%.