TU-12EX: Chromatic Tuner. Chromatic Tuner for Guitar & Bass. This successor to the legendary TU-12 provides BOSS" famous needle/LED indicators for fast, accurate tuning. Other features include Flat Tuning of up to six half steps, ACCU-PITCH with an audible beep, a reference tone, a built-in microphone for acoustic instruments and battery-saving Auto-Off.