I've tried googling but I guess I am not getting the wording right because I'm not finding what I'm questioning.

So, I'm fairly new to opks..I got lucky last month and the first one I took was positive. This month not so much. So question is..do they kind of work on a gradient? Like the line is faint then just before ovulation its dark for positive and then gets lighter with each passing day? Or do you just get thr surge and thats it...like its not gradual?

Glow says I'm supposed o today..but opks are telling me something completely different. The first time I took one (because I was expecting to O today) was Sunday..and that one was very close to positive. Test line was maybe half shade lighter..but so close in a picture probably would have looked the same..and every day since at the same time..it seems to have gotten lighter and lighter?