May 31, 2015. Difficulty fell by -2.50% to 47.59B from 48.81B.
Change
-2.50%
New difficulty
47.59B
Period length
14.4 days
Network hashrate then (7-day)
0.3 EH/s
Bitcoin price then
$232
Hashprice then
$2,486/PH/day
The 2,016 blocks before it took 14.4 days, longer than the 14 intended, so hashrate had fallen, and difficulty fell by 2.50%: an ordinary adjustment. For every machine on the network that is a pay rise of the same size until the next retarget.