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Browse to the data file by clicking on File -> Open, navigating to the directory where the file was saved, selecting the file, and pressing Enter.
If you are asked which plugin to chose for opening the file, choose org.lcsim. This query may or may not appear on your system. (It only shows up if you have multiple plugins installed that can open the file.)
JAS has changed a bit now that the LCIO file is loaded.
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