I have been using a cassette style test at around midday from day 10 of my cycle. I can test with nothing for days then start getting lines which are fainter than the control colour, but on my instructions this is classed as a negative. Glow tells me I'm ovulating and everything would suggest I'm ovulating but the test comes up negative for a couple of days then goes altogether again. On the days I suspect I'm ovulating I do about 3 tests and they all come up with 2 lines but the test line is technically 'negative'.