I really think you (and others in the thread) are missing the point of the new research and this estimator - built on the back of that research and best-fit analysis within a model informed by 160,000 candidates.
The old way of teling ones class was based on things like parents, profession, capital.
This is a supposed new, more refined classification system updated for modern times; times where social mobility is vastly greater than old times, and that new cultural pursuits and arrangements mean that it is not so simple as upper, middle and working anymore.
The researchers believe that your social circle and activities are (for example) more accurate and realistic indicators of your class than the old notions of what your parents did or did not do. That's why it does not ask you what your parents did. That's why it does not ask you what you do.
I'm not saying the calculator is right or wrong or if the research is flawed or not, but I am saying that responses like 'well coming from parents Y and from location X this seems like a pretty inaccurate calculator' is not appropriate.
I'd say the researchers are flawed, they are skewing too much towards socialising. Those of us that choose not to be social get penalised on their class rankings.