You are flying at a constant altitude according to your altimeter. Your altimeter setting is unchanged. Which of the following interact to give a minimum a true altitude?

1. Flying from an area of low pressure to that an area of high pressure.
2. Flying from an area of high pressure to that an area of low pressure.1,
3. Flying from a warm air mass to a cold air mass.
4. Flying from a cold air mass to a warm air mass.