When someone thinks something is funny, how accurate are they? How can someone measure how funny a movie or a joke is? Can you measure that by the amount of time spend laughing or the amount of 'smiling' the person does as a result of hearing the joke? Conscious understanding of our own feelings is subjective. That information also means that all conscious understanding is subjective - when someone thinks they understand something, they are going to bias it in some way.
What if someone tries to be as objective as possible when making all of their decisions. Then possibly all decisions that are objective in the first place (non-emotional decisions) and not subjective might be fairly non-biased. But then what types of assessments are non-emotional and which types are emotional? Math isn't emotional - scientific fact isn't emotional. That isn't to say that there isn't a type of bias someone has when they do addition. Maybe they are thinking about something else at the same time and this biases possible interpretations of the objective data.
So it is clear that something objective is objective, and something subjective is subjective, however how could someone measure differences in how subjective something is?