What is the saying that explains the altimeter's behavior with changing pressure?

The saying "High to Low, Look out below" and "Low to High, plenty of sky" accurately describes how an altimeter responds to changes in atmospheric pressure and helps pilots understand altitude variations.

When atmospheric pressure decreases, the altimeter indicates a lower altitude than the actual position. Thus, when pilots see a low-pressure area (indicated by the first part of the saying, "High to Low"), they need to be aware that they may actually be at a higher altitude than what the altimeter is displaying, which can lead to the risk of flying lower than intended ("look out below"). This understanding is crucial for maintaining safe altitude during flight, especially when navigating near terrain.

Conversely, when pressure increases, the altimeter will read a higher altitude than the actual altitude. The second part of the saying ("Low to High, plenty of sky") reminds pilots that as they transition into a higher pressure situation, they may have more altitude cushion available, implying that there is more space above them.

This saying serves as a helpful mnemonic for pilots to remember how to interpret their altimeter readings in relation to atmospheric pressure changes, ensuring they can respond appropriately to prevent altitude-related issues.