Mining difficulty adjusts automatically every block. The graphs below show the difficulty time series for the last 4 weeks worth of blocks (20160 blocks).
The adjustment aims to maintain an average block-mining time of 2 minutes.
A growth in the difficulty indicates that the average block-mining time during the last block(s) was less than 2 minutes (due to more miners joining the network and 'searching' / 'mining' for blocks).
A drop in difficulty indicates miners have left the network so finding each block is adjusted to be 'easier' for the smaller number remaining.
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