The Seiko SQ50V is one of the most popular metronome on the market. 

It features a new look, easy operation tempo dial, adjustable volume, two selectable click tones (high and low), and two tone generators (A and Bb). Dial-in virtually perfect tempo settings and an A=440 tone for tuning. Tempo range from 40-208BPM can be set easily from the 39-position rotary dial. A red LED can be selected for a visual beat or combined with a click sound for visual and audible beat-keeping. Includes earphone jack.