This is meaningless without considering the granularity of the unit of measure. Most people are of average height when measured to the nearest meter. The motivation behind the measurement determines the granularity -- for a cockpit, the seat and pedals and stick probably have to be within a couple of inches of tolerance. For a society, how racist or treacherous or murderous does a person have to be before we no longer accept them in society?

I think there are simple guidelines: first, make clear the distinction between public and private spaces. No mandatory or secret surveillance in private places. Second, informed consent and transparency: Those willing to give up privacy for convenience within private spaces must have access to (but not be forced to read) clear, understandable, honest descriptions of what their information devices are doing.