The kids figured approximately 99-100 drops per 5 ml using standard syringes. These are the ones I got when they were young for measuring medicine from the pharmacy.
They double checked their work for the various tests by using standard 5ml to whatever drops the tests called for. Then tested multiple tanks/times and came up with identical colors.
Obvious, drop size is variable depending on whether your using a turkey baster vs different sized syringes. But once you get it down all you need to do is etch new lines and forget about it.
The old ph tests back in the day, was measure 3/4 of the vial by eyeballing it and adding 1 drop. In doing that multiple times they came up with 33 drops...which checks out to the now 3 drops of PH solution to the 5 ml of water(99 drops). We had an old kit my mom had and that's why they got the whole notion of getting it down to 1 drop.
Whatever someone's using...all they need to do is figure out how many drops fills up for standard 5ml and then do the math/ratios to get it down to 1 drop. Nitrite 1 drop solution to 20 drops water(w/ syringe we use or approximately 1 ml)...it's pretty basic math conversions.
It's all good-they can test to their hearts content and I'm not wasting $$$.