Redundant metric units
Part of my units pages
The term “metric” is sometimes used to refer to the SI system, but the two differ slightly. In particular, day-to-day use of metric can often involve extra units which are not part of SI. Sticking to SI units avoids the following redundancies:
The “tonne” is just a megagram.
The litre is a stupid unit: it’s 1 milli-cubic-metre. The only reason to avoid cubic metres seems to be the unwieldy name, but other languages have solved this with names like “stere” and kuub. Cubic metres may seem quite large for everyday quantities like drinks, but it’s already common to use phrases like “700 mill bottle” (700ml = 0.7litres). The same works with cubic metres, with a litre bottle becoming “one mill” and 0.7litres becoming “700 micros”.
Metric temperatures are usually given in Celsius or Centigrade (those are the same thing!), which can be positive or negative. Since there is an “absolute zero” temperature, we can avoid false numbers by choosing absolute zero as our starting point. If we count “degrees Celsius starting from absolute zero”, we get the Kelvin scale, which SI uses.