I'm really wondering where those massive swings come from... +15 PH in a single day, and -15 PH the other day. That would be 15000 miners of the newest 1 TH generation hitting the network and then vanish again.... perhaps manufacturers "testing" their costumers hardware before shipping?
I've been pretty surprised to see the swings as well - I don't think anyone has come up with a great explanation for such a large swing besides new hardware manufacturers testing equipment (and luck of course). I certainly can't think of one.
