If you're tempted to crack it open, remember they always have three lines on them. However, I don't know if you can glean anything from line 'progression' from these if you use another at some point if it also says 'not pregnant'. This cycle I used a few, four I think, the first was faint, the next was darker and the third the darkest, before the fourth was barely there again. I'm assuming this means it was in fact picking up hCG, but not quite enough to turn it positive as I had a number of positive regular tests varying from 10, 12.5 & 15mIU