What is an altimeter ? State its principle. How is its scale calibrated?

Explanation

### Step-by-Step Solution:

**Step 1: Define an Altimeter**
An altimeter is a device used to measure altitude, which is the height of an object above a reference point, typically sea level. It is commonly used in aviation and mountaineering.

**Step 2: Explain the Principle of an Altimeter**
The principle of an altimeter is based on the relationship between atmospheric pressure and altitude. As altitude increases, atmospheric pressure decreases. An altimeter measures this change in pressure to determine the height above sea level.

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