Girls, explain? Cycle is 30 or 29. Just judging by ovulation tests, it…

Girls, explain? Cycle is 30 or 29. Just judging by ovulation tests, it was on Day 14, but the calendar shows my type should be on Day 17. But I have this feeling that even the tests are misleading on Day 15. I take a test and the second strip is already very pale, today I did another one too, also pale... Although today it's really pulling down low... Nothing makes sense, can't it just show up like that first day, then a new test and almost invisible?)