Works well on an iPod Touch 4th generation using iOS 5.0.1 ... simple, sweet, obvious. It includes the octave number with the base note (C3, C4, F#3, etc.) and uses a red/green color code to let you know when you are in the ballpark. It even included the tunings for several string devices and even some alternate tunings for hammer dulcimer, guitar, etc. and displays those at the bottom of the meter display. I originally bought Tuner Pro (that shows the actual frequency and a rotating lower dial) but this one uses a "cleaner" sample rate so can get you tuned faster since you dont see a dial "swinging in the breeze". The only "down side" is that this app is iPhone/iPod Touch only (no iPad yet). Well worth the 99 cents and wish I had found this one when it was free.