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The Group Options frame allows the user to define a series of groups of drifters with a user defined ID, set with the New button. For each group the release and end days, as well as settling velocity, may be defined by the user. The settling velocity may be positive (downward) or negative (upward)is always downward. When the Clear Group button is pressed all the user defined particle groups will be erased. The Clear All button will remove all of the seeds for all of the groups.
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