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    Hmm, could you be more precise about the "time stamp" used? Afaik the time in the block header can be very inaccurate, and block propagation can induce some delay between nodes (so, if they record the time they first heard of the block, not everyone would exactly agree on the same difficulty). And, what would happen if one generated blocks with a computer whose clock is out-of-sync (like, days in the past/future)? (If this is not adequate as a comment I can make a separate question.) Commented Sep 10, 2011 at 19:30
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    @Artefact2: from the wiki: "A timestamp is accepted as valid if it is greater than the median timestamp of previous 11 blocks, and less than the network-adjusted time + 2 hours. "Network-adjusted time" is the median of the timestamps returned by all nodes connected to you." Commented Sep 10, 2011 at 21:55
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    @billpg - Correct. It would be more accurate to say difficulty is set by the algorithm. It is adjusted every 2016 blocks based on average execution time for prior 2016 blocks to ensure future average execution time remains ~10 minutes. Of course a miner could ignore/break this algorithm but then they wouldn't be mining valid bitcoin blocks (they would be mining a fork). Commented Oct 10, 2011 at 13:20
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    Just to be completely clear: "time the past 2015 blocks took" means "Timestamp of block 2016N-1 minus timestamp of block 2016N-2016"? And without the off-by-one bug, it would have been block 2016N-2017? Commented Jan 22, 2012 at 6:09
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    There is no rule that requires a specific number of transactions to be put in a block. This question and answer is about proof of work in blocks, not transactions. Commented Mar 7, 2019 at 17:54