I think the drops are of uniform size as the hypo needle is cut square to its axis (i.e. not sharp) with no burrs inside or out so surface tension should enforce consistency.
I'm not trying to convince you that they aren't - just throw some things out for you to think about.
Ummm. I'm color blind but when I look at the instructions for bromcresol green methyl red indicator used in alkalinity tests they say titrate to one color for one value of pH and another for another depending on which definition of alkalinity you are using. These would all look the same to me and even people with normal color vision have different levels of acuity. Also, the shapness of the calmagite endpoint depends on magnesium being present and on pH (a buffer is usually added to insure that the pH is correct) etc. In any event when you are using an indicator you are asking for a human to make a judgement and humans aren't always consistent in that. Fatigue, the color quality of the light being used to make the determination, the angle of subtense of the object being looked at all have an effect on how we perceive color. None of these may have an appreciable effect but in general an instrumental method is always preferred. With alkalinity you have the possibility of using a pH meter. With hardness you don't. There is an instrumental calcium/magnesium hardness test but the instrument is a sprectrophotometer.The color changes are sharp and rapid. I also was under the impression that these indicators had very consistent pH transitions points.
The collaborative study is interesting, but one would need to be somewhat assured that all investigators had consistently good experimental technique.
In such a test you are measuring the method and the analyst. If a method gives a high CV intra lab then the chemistry itself is too variable. If it has a decent intra lab CV but a high inter lab CV then analysts are too variable (for this method).
I guess the cleanest method would be for me to carefully measure a water sample (multiple times to observe my own variation) and then have the same sample measured by an outside lab that would provide error bars about their measurements.
That's a good idea but it would be better if someone else put together the test sample without telling you what (quantitatively) is in it. Also, it should be made up with standardized chemicals (available from Hach and others) using Class A glassware dunked in a water bath etc. Quantitative analysis is a fascinating subject but there are lots of things to consider.