I had the same problem with the ovulation kits that use the "two lines". The test line should be as dark as, or darker than the control to be considered (+). I have switched to the kits that use the smiley face or empty circle to indicate (+) or (-) test. There is no guessing involved. It is either :) = (+) or 0 = (-). If you are still wondering and want to know for sure, get one of these and you will have your answer.
go to peeonastick.com and they have tons of pics to show + & - ones