Oxygen is a major and vital component of the Earth atmosphere representing about 21% of its oomposition. It is consumed or produced through biochemical processes such as oombustion, respiration, and photosynthesis. Although atmospheric oxygen is not a greenhouse gas, It can be used as a top down constraint on the carbon cycle.The variation observations of oxygen in the atmosphere are very small, in the order of the few ppm's. This presents the main technical challenge for measurement as a very high level of precision is required and only few methods induding mass spectrometry, fuel cetl, and paramagnetic are capable of overooming it. Here we present new developments of a high-precision gas analyzer that utilizes the technique of Cavity Ring-Down Spectroscopy to measure oxygen concentration. Its compact and ruggedness design combined with high-precision and long-term stability allows the user to deploy the instrument in the field for continuous monitoring of atmospheric oxygen level. Measurements have a 1-sigma 5-minute averaging precision of 1 ppm for 02 over a wide dynamic range of 0-40%.