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This doesn't come anywhere close to 1900MH/s, so it seems there's a lot of hashrate that is missing.
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Actually, from my understanding, the hash-rate is determined using difficulty, and time to find a a block. So its not directly taken from whatever is connected and what they are reporting.
So it will take a day or two for the difficulty to adjust and then hash-rate will be known.
Interesting explanation, and not something I've heard before. I'm not saying I disagree with it - because I don't really know, frankly - but when Monero forked there was a sudden - near vertical - drop in hashrate; difficulty, however, took another day or so to adjust downward.
That is because Monero's difficulty adjustment algorithm takes several blocks to adjust with the network hashrate. iirc it takes 720 blocks for Monero to adjust the difficulty according to Network hashrate (it's not linear tho)
Difficulty in fact is dependent on Network hashrate. It depends on coin to coin and what difficulty adjustment algo they use.