| Date | Value |
|---|---|
| Jul 24, 2017 05:15 | 350 ppm |
| Jul 20, 2017 11:25 | 360 ppm |
| Apr 9, 2017 07:39 | 400 ppm |
| Mar 6, 2017 04:48 | 450 ppm |
| Feb 28, 2017 04:10 | 480 ppm |
| Feb 12, 2017 09:59 | 470 ppm |
| Dec 18, 2016 05:43 | 460 ppm |
| Nov 15, 2016 12:43 | 460 ppm |
| Oct 26, 2016 12:31 | 430 ppm |
| Oct 16, 2016 09:06 | 420 ppm |
| Oct 1, 2016 08:02 | 420 ppm |
| Sep 23, 2016 08:13 | 390 ppm |