So the difficulty decreases sometimes? I was under the impression that it only went up-and-up-and-up.
How is the difficulty set? Is it set by the number of leading '0's required for a block solution? Who sets the difficulty? Is it the nodes?
A) The difficulty can decrease if the average block time over the most recent 2016 blocks is >10 min
B) Difficulty is set via mathematical forumal dependent on the time taken to solve the most recent 2016 blocks.
C) The difficulty determines the number of leading zeros required for a valid block solution.
D) The bitcoin protocol sets the difficulty itself.