I think that these tests are way more tolerant that instructions make it. It is just that there is not much downside in being overly precise. Even if the tests

I think that these tests are way more tolerant that instructions make it. It is just that there is not much downside in being overly precise. Even if the tests can work if you add between 1 and 100 drops, if you are told to add between 1 and 100 drops, what are you going to do? 1? 10? 50? 100? open the vial and eyeball it? It creates unnecessary confusion. So you just say "add 10 drops", not because you need exactly that many, but because it is the instruction that will make it the least likely to screw up. It is the same for cooking recipes. The two ways to not screw up is to follow the recipe to the letter, or to understand the underlying idea. The latter requires some experience in cooking. Covid self tests are intended for people with no experience, so, they make you follow the recipe to the letter.