Wittgenstein's ruler comes to mind: what is 'productivity' measuring?

A quick glance at the chart in the article suggests that the variance of this metric is huge. It is more or less a white noise source with a small DC offset. Given the formula the BLS uses, I would be hard pressed to calculate my own productivity (outside of lawyers and people working on assembly lines or at fast food establishments most people do not keep track of their hours). If I can't measure my own 'productivity' then I have no idea how the hell the BLS is going to do it.