How? By having > 10minutes per block average during the 2016 blocks generated (number, not year) as below:
Date Difficulty Change Hash Rate
Jun 04 2017 678,760,110,083 13.90% 4,858,754,124 GH/s
May 23 2017 595,921,917,085 6.42% 4,265,775,241 GH/s
May 10 2017 559,970,892,891 7.28% 4,008,427,786 GH/s
Apr 27 2017 521,974,519,554 0.22% 3,736,439,151 GH/s
Apr 13 2017 520,808,749,422 4.24% 3,728,094,244 GH/s
Mar 30 2017 499,635,929,817 5.03% 3,576,533,297 GH/s
Mar 17 2017 475,705,205,062 3.24% 3,405,230,497 GH/s
Mar 03 2017 460,769,358,091 4.54% 3,298,315,540 GH/s
Feb 18 2017 440,779,902,287 4.41% 3,155,225,442 GH/s
Feb 04 2017 422,170,566,884 7.43% 3,022,014,630 GH/s
Jan 22 2017 392,963,262,344 16.64% 2,812,940,600 GH/s
Jan 10 2017 336,899,932,796 6.05% 2,411,623,656 GH/s
Dec 28 2016 317,688,400,354 2.43% 2,274,102,150 GH/s
Dec 15 2016 310,153,855,703 8.16% 2,220,167,778 GH/s
Dec 02 2016 286,765,766,821 1.76% 2,052,749,317 GH/s
Nov 18 2016 281,800,917,193 10.68% 2,017,209,539 GH/s
Nov 05 2016 254,620,187,304 0.40% 1,822,642,296 GH/s
Oct 22 2016 253,618,246,641 -1.90% 1,815,470,125 GH/s
Oct 08 2016 258,522,748,405 7.17% 1,850,577,916 GH/s
Sep 25 2016 241,227,200,230 6.82% 1,726,771,560 GH/s
Sep 12 2016 225,832,872,179 2.30% 1,616,574,667 GH/s
Aug 29 2016 220,755,908,330 1.56% 1,580,232,344 GH/s
Aug 15 2016 217,375,482,757 7.67% 1,556,034,316 GH/s
Aug 02 2016 201,893,210,853 -5.43% 1,445,207,896 GH/s
Jul 18 2016 213,492,501,108 0.04% 1,528,238,850 GH/s
Jul 04 2016 213,398,925,331 1.88% 1,527,569,009 GH/s
Jun 21 2016 209,453,158,595 6.83% 1,499,324,110 GH/s
Jun 08 2016 196,061,423,940 -1.63% 1,403,462,340 GH/s
May 24 2016 199,312,067,531 2.60% 1,426,731,353 GH/s
May 11 2016 194,254,820,283 8.73% 1,390,530,167 GH/s
Apr 28 2016 178,659,257,773 -0.01% 1,278,892,782 GH/s
Apr 14 2016 178,678,307,672 7.09% 1,279,029,147 GH/s
Apr 01 2016 166,851,513,283 0.82% 1,194,369,655 GH/s
Mar 18 2016 165,496,835,118 4.46% 1,184,672,491 GH/s
Mar 04 2016 158,427,203,767 -3.10% 1,134,066,098 GH/s
There's a few in there with negative diff adjust! That being said, the long term trend is up, up, and away...!!