The correct answer is P= Pressure
Step-by-step explanation:
Pressure refers to the force exerted over a body, this force is usually measured using the formula F (Force) / A (Area). In the case of the barometer, this instrument's purpose is to measure the air pressure or the force the atmosphere exerts over elements. For doing this, the barometer uses units such as atm (standard atmosphere pressure unit) or Pascal (Newton /square meter). Additionally, the pressure detected by the barometer changes with altitude, temperature, and climate factors. According to this, the letter that should be used for a barometer is "P" as this instrument only measures pressure.