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Regarding your question, can you provide a MERRA-2 document or web page where the term "bin" is used? Bin commonly refers to a data storage location in which all valid observations for a particular spatial resolution are kept, until averaging over a time period is performed to provide a value for a gridded data product. So it would be helpful to know the context in which the term "bin" occurs. We can consult with our MERRA-2 data experts once we have such information from you.