The Boss TU-2 is a guitar tuner. It is favored by guitarists for its uncharacteristic stompbox shape that allows it to fit with other compact pedals, and allows for fast, accurate tuning at gigs. It can tune to standard tuning on guitars and basses, and to flat and double flat standard tunings for both bass and guitar. As the name states, it also operates as a chromatic tuner. The series of indicator lghts on its face can either strobe in the direction the head should be turned, or a green light in the middle indicates an in tune note. These modes can be toggled between with the "stream/cent" button. Different tuning styles can be cycled through using the "Mode" button. A digital display below the lights reads which string is being tuned. It goes from 6 is E, 5 is A, etc.
There are input, output and bypass jacks. If the output jack is used, the signal to the amp will be cut when tuning, allowing for silent tuning. when the bypass jack is used, the signals continues through without being interrupted, so the guitarist can hear themselves while tuning. It also has an "out" AC power jack that lets guitarists daisy chain their pedal board with a single cable that powers multiple pedals.
Like all of Boss's compact pedals, it can run on both AC power or battery power using a 9 volt battery.