January 8, 2013. Difficulty rose by +9.06% to 3.25M from 2.98M.
Change
+9.06%
New difficulty
3.25M
Period length
12.9 days
Network hashrate then (7-day)
—
Bitcoin price then
$14
Hashprice then
—
The 2,016 blocks before it took 12.9 days instead of 14, so the network had more hashrate than the difficulty assumed, and difficulty rose by 9.06%: a large adjustment. For every machine on the network that is a pay cut of the same size until the next retarget.