For the OPK to read positive the line has to appear as dark or darker than the control line (control line = the line nearest the green bit on the OPK). If the line appears lighter or no line at all, the test is negative and you're not likely to be ovulating (as in your picture). When you see the positive line, you will probably ovulate soon and this is your most fertile time. Hope this explains it. I used OPKs and got pregnant on the second month! You need to test about 3 times a day to make sure you catch your fertile window. Good luck. x