So I've been charting for three months (ttc for 4) and this is the first cycle I've been confused about when O is happening. If I use the "advanced detector" FF puts O at CD 18. If I use the FAM detector, it puts it at CD 16. I'm inclined to think it was CD 16 bc my coverline in previous cycles was never above 98.0 and my temps in the week before O are always 97.9 and below, and usually a couple points lower than that right around O. But honestly I haven't been doing this long enough to know! So when do you think I O'd??? Any help would be appreciated!!