This course focuses on the physics of the atmosphere and its consequences on speed and altitude measurements. At the end of this course, you will understand precisely the meaning of the speed and altitude indication available to the pilot of an airplane. You will understand the difference between standard and actual atmosphere and be able to perform basic altitude and speed correction computations. You will understand why jet airliners need to be pressurized, or why a clogged Pitot tube can mislead a pilot. Although some math equations are used from time to time to justify certain results. This course insists on curve shapes, figures, tables, and you can efficiently follow it while skipping the equation-solving parts if you do not fancy them. This course is a part of the specialization "Fundamentals of Flight mechanics".