One of the more advance piezo clip-on tuners on the market that even comes with a built-microphone! You can switch between four modes of tuning- guitar, bass, violin and chromatic (for use with most other acoustic and electric stringed musical instruments). The whole display is green when you"re in tune, and is red when you"re out of tune. It automatically shuts off after 5 minutes to save your battery. Great for "open" tunings, down tunings, transposing, detuning since you can change the calibration. Batteries included!