Is the line dark enough???

Lauren

I need a little clarification. On the ovulation predictor tests, isn't the second line suppose to be as dark as the control line?

I've been using them for a few months now and my second line is never as dark as the control line. Around when glow says I'm in my fertile window I get 2 or 3 days where it's darker than normal, but if I'm only ovulating one day how can that be?