- Model Name: Dr. Rhythm DR-550 - Brand: BOSS - Tempo: 80 - Pattern: 1 - Song: 5 - Function: Rhythm Machine - Buttons: Start, Stop, Tempo Adjustment, etc. The main unit is the only item included, so operation has not been confirmed. The battery cover is missing. This item is being sold as junk. Instant purchase without comment is OK. Price is not negotiable. The photos are everything included. Please consider this item understanding that it is junk.