How about the following scales? Are they also an issue? - Time (Calendar) relative to either anno domini or Unix time? - Position Coordinate relative to Greenwich? - Electric Potential relative to earth potential? - pH, pKa, pKb scales relative to a neutrality of 7? - Decibels, phon and sone relative to threshold of human hearing? - Pressure (hydraulic or blood) relative to atmospheric pressure? - Altitude relative to sea level? -> For pressure and altitude there are lots of other scales, e.g. used in aviation - Richter scale relative to detectable earthquakes? - Beaufort relative to calm wind instead of zero wind? - Borg physical exertion not starting at zero?