I've started using them for the first time one month ago. My cycle is pretty regular, 28 days, and it tells me to start testing on day 8. Two days of an empty circle, followed by 4 days (+/- 1 day) blinking smiley before static smiley appears. When I take the stick out of the indicator to look at the lines, I can't see a clear progression though. That makes the cynic in me wonder....do they actually work or do they make an educated guess? After all, predicting that the fertile window starts on day 10 of a regular 28 day cycle and that ovulation will occur a few days thereafter would probably lead to a high accuracy rate either way.