What does these lines mean ?

Giulia • May 23 2019 👼🏼

I don’t always have the 2nd line in my OPK. See pic (some days before the LH surge is missing the second line)

But these past few days (DPO 8-10), I was just curious so I took out the OPK to test again and saw all the 3 days has 2nd line.

Just wondering if anyone knows if it means something ?