An oxygen analyzer is used to confirm the concentration of oxygen you are breathing. The Expedition-X is easy to calibrate and uses an external Teledyne oxygen sensor, which lasts about 3 years. It comes in a compact, water resistant case, and includes a backlit screen for easy reading in the dark. The supplied sampling tee (blue) fits in-line with the air delivery hose for direct measurement. Also can be used inside the Snowcap or other altitude tent. Includes carrying case, oxygen sensor, cable, sampling tee, and instructions.