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This one answers your question:
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For current members, your initial merit score is equal to the minimum required to your rank. Of that, a certain amount (less than the usual half) is spendable. The spendable amount was calculated based on your current rank and the number of activity points you earned in the last year. A Legendary member who hasn't posted in the last year would still be Legendary, but would not have any spendable merit.
If someone sends you 1 merit, the 0.5 sMerit is not wasted; it is just not shown until you get another merit point.
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For more details, please read this one that was posted by Theymos (forum's admin)
https://bitcointalk.org/index.php?topic=2818350.0