One of these is specificity, meaning by if it is specific, one may be able to measure it. Of course there is only a necessary condition and not a sufficient condition.
The other one is unambiguous. There are different people who are operating this one, so all of them must have the same meaning, which means it must be unambiguous.
Finally the parameter is a measurable one. When we say, it is some sort of a quantity to measurement to quality measurement, on a 0.5 scale, or 0.3 scale, or "n" scale. So we must be able to quantify the things.
