TuneLab, the popular piano tuning software that has been used since
2008 by professional piano technicians around the world, is available
for iPhone, iPad, and iPod Touch. You can find the app in the App Store
by clicking here:
Here is what the main tuning page looks like:
The bar with the black squares is called the phase display. The
squares move left for flat and right for sharp. You tune the piano
so that the pattern comes to a stop. This display is for
fine-tuning.
Near the bottom is a graph called the spectrum display. This
display gives additional information about the distribution of sound
energy across the frequency spectrum. If there are several pitches
sounding at once, this graph will show a peak for each pitch.
Using this you can do a rough pitch-raise tuning without spending time
moving mutes.
The best way to learn all about TuneLab for iPhone is to download the
manual right here: