Lines on the Lunette... and flow question

You know the lines at the bottom of the Lunette (the end where the stem is)?  Does anyone know how much fluid each line represents?  Has anyone figured this out?  I'm trying to figure out how much I'm actually filling this cup and it seems like I'm never making it past that line (even after not emptying it for 12 hours on my two heavier days).  Do I just have a really light flow?  Is that normal?

I have the larger Lunette, btw.