Please don't place too much on how dark the lines are on tests, its not reliable, the tests are designed to see if there is HCG in your urine or not and nothing else. The HCG on your urine can fluctuate substantially depending on various factors, in addition there are different amounts of dye in each test. I tested until I got a decently dark line (still lighter than control line) and just left it. I know from experience that sometimes in a non viable pregnancy you can get very promising results from doing repeated tests but in a viable one things are more ambiguous and worrying. Xx