The OMNI instrument is a virtual instrument representing the collection of Magnetometers, Electrostatic Analyers, and Energetic Particle instruments used in the creation of the OMNI datasets. The instruments used within the OMNI datasets come from the ACE, Wind, IMP8, Geotail, GOES and various other spacecraft. For any given time period OMNI uses a selection criteria to select the "best" available data to be used. Thus, only one magnetometer, one electrostatic analyser, and one energetic particle instrument are used for each data point within an OMNI dataset. Without looking at each data record it is not possible to tell which instruments contributed. As result, the OMNI instrument is used as a proxy for the set of possible contributing instruments.