The Korg MM-1 MetroGnome fits comfortably on your ear so only you can hear it. Sets tempo over a range from 40-208BPM. 1/4, 2/4, 3/4, 4/4, 5/4, 6/4, and 7/4 time signatures. Duplet, triplet, and quadruplet beats. 50-hour lithium battery for cable-free use. .64"W x 1.83"L x .66"D.