I was reading Claymore's GPU miner thread and saw this, "current developer fee is 2.5%, miner mines 39 rounds for you and 1 round for developer."
What is a mining round?
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I believe this refers to hashes - it does 39 hashes for you and 1 hash for the developer, regardless of whether the hashes are valid or not. As Claymore is closed source, we can't easily verify this, but from what I have seen running the miner it seems like the most likely explanation.