Metronomes: Devices that produce a steady, rhythmic beat (click) to help musicians keep accurate time and rhythm during practice.
Clip Tuners: Devices that detect the frequency of sound and guide the musician to accurately tune the strings or notes of their instrument so that it is properly tuned.
Tuning Forks/Pitch Pipes: Metal tools in the shape of a fork (or small whistles) that, when struck, produce a stable, pure reference note (usually A) for tuning by ear.