Opk question & kit

Today starts my first day using OPKS & I'm on Cd 7.  My periods are irregular (ranging from 28-39 days) so I decided to start using them early vs. late.  My question comes with documenting the result.  The icons show 1 line or 2 lines.  I understand OPKS are only positive if the test line is darker or equal to control line, so is that the only time I choose the 2 line icon? Just want to make sure I'm using the app correctly. Thanks in advance for feedback.