Altimeter is a device to measure _________.
a: Temperature
b: Height
c: Altitude
d: Rainfall

Hint: A device which measures a physical quantity is called a measuring instrument. There are various kinds of instruments which measure different physical quantities namely height, altitude, time, temperature and rainfall. These instruments are barometer, altimeter, anemometer, astrolabe and caliper etc.

Complete Step by Step answer: Option a: A physical quantity which expresses hotness or coldness is called temperature. Thermometer is a device to measure temperature. There are various scales to measure temperature namely celsius scale, fahrenheit scale, kelvin scale. Altimeter is not a device to measure temperature. This is the incorrect answer.
Option b: A measure of vertical distance is called height. Stadiometer is used to measure the height of human beings. Altimeter is not a device to measure temperature. This is the incorrect answer.
Option c: The vertical elevation of an object generally above a sea level is called altitude. Sometimes altitude is also known as height or depth. The reference of mean sea level or local ground level is used to measure aviation altitude. Altimeter is a device to measure altitudes. This is the correct answer.
Option d: The form of drops which have condensed from atmospheric water vapor and become very heavy. These droplets fall under gravity are called rainfall. Precipitation gauges is the device which measures rainfall.

Option c is the correct answer to the above question because altimeter is a device to measure altitudes.

Note: The pressure altimeter operates on the principle that average atmospheric pressure decreases linearly with the decrease of altitude.