I have been mining for a few months, the calculated hashrate was always very close to the reported hash rate until about a week ago. Now is much lower. I was mining on two computers and have the same problem on both. I tried deleting the dag files as well as deleting the chaindata files for geth but it did not make a difference. I am using EthMiner v0.9.41 , Geth 1.4.10 , mining on nanopool. Anyone have any idea what the problem is?