It makes no sense to test a couple of days after intimacy, because it will take at least 5-7 days for the egg to implant, and then it still takes time for hCG to reach a normal level. With a premature study, it may turn out that a second white or very weak strip will appear. Therefore, it is advisable to conduct such studies after a delay.
Each pregnancy test has two sectors - indicator and control. When the required volume of urine enters the control sector, a reaction occurs and a bright line appears. This is a confirmation that the test is working and of high quality, and the study is proceeding correctly. The indicator sector performs the main function - it determines the absence or presence of an interesting position.
If there is no pregnancy, then only one strip appears, but if the girl will soon be a mother, then 2 strips appear, which should normally be as clear as the control one. If the second strip is light or blurry, then it cannot be regarded as a sign of conception. You will need to retest in a couple of days. A barely noticeable second strip of a grayish tint indicates an incorrect reaction of the device to the test urine, so this test is faulty and cannot be used for research.