First time using ovulation test. ??

Ashley
This is our second month ttc. I am using the ovulation strips.  I started check my ovulation on Wednesday and my fertile window just started yesterday. The test line sometimes looks like it's getting darker then some days you can barely see it.  Today both test lines are barely visible
Question. Is the line supposed to darken each day as I get closer to ovulation ?  Or does it just become darker when I ovulate ?  I guess I assumed the line would become darker each day and not back and forth.