What is the purpose of the Kollmans window in a sensitive altimeter?

The purpose of the Kollmann's window in a sensitive altimeter is to allow pilots to adjust the indicated altitude based on the current altimeter setting. This adjustment is crucial because atmospheric pressure can vary with weather changes and changes in altitude. The pressure applied to the altimeter determines its reading; therefore, if the altimeter setting (commonly referred to as the barometric pressure setting) is not correctly adjusted to match the current atmospheric conditions, the altimeter will not display the correct altitude.

When pilots fly from one area to another, especially where pressure changes are significant, they need to ensure that their altimeter reflects the local pressure by making the necessary adjustments through the Kollmann's window. By doing so, they can maintain safe altitudes and comply with airspace requirements. Thus, this feature is key to ensuring accurate altitude readings for various phases of flight.