The piano?
The stethoscope.
This instrument is called a stethoscope.
your voice
The Stethoscope is used by Doctors to hear heart beat sound of the patient.
the banana but you didnt hear it from me
The zero error helps in correcting the misreading you get from any instrument. It helps in maintaining the sensitivity of the instruments.
the brain helps you to tell you what you hear
The bell helps to project the sound of the instrument out better.
A stethoscope where you can hear the sound of someones heart.
barometer
The most commonly-used instrument is a stethoscope.