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3) Time Since Last Read (20% of the score, by rank of the most recent read among most recent reads for all datasets)
If Example: if there are 10 datasets, they are sorted based on time since the last time the dataset was read. The dataset that was read the most recently gets 10/10 * 20 = 20 (rank / total datasets * 20) points, as its it's ranked first. The second most recently read dataset receives a score of 9/10 * 20, the third most gets 8/10 * 20, and so on. As time since the last read can vary from never to 0 to a very large number, a relative score seems necessary.
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