Comment Re:US Metric System (Score 1) 1387
"0 C - point at which water freezes, 100 C - point at which water boils.
Yep, totally arbitrary. Lets not even start with Kelvin."
Just picking at nits, but, the standard boiling point of water was 0C on the original scale devised in 1742 by Anders Celsius, then 100C from 1743 until 1954 when degrees Celsius were re-defined by the triple point of Vienna Standard Mean Ocean Water; then, 99.97C until 1982, at which point it became 99.61C, since the IUPAC decided 1 bar (100kPa) would be a less arbitrary than 1 atm (101.325kPa) as the way of defining standard boiling point. The current definition of Celsius is:
* -273.15 is absolute zero
* 0.01 is the triple point of VSMOW
Those temperatures mentioned above (99.97 and 99.61) are from one wikipedia page (http://en.wikipedia.org/wiki/Boiling_point#cite_ref-7) but the VSMOW page (http://en.wikipedia.org/wiki/Vienna_Standard_Mean_Ocean_Water#cite_ref-2) suggests the melting point of VSMOW is 0.000089(10) and the boiling point is 99.9839, although ITS-90, used to calibrate thermometers, actually uses 99.974. So, I'm not sure where the 1982 IUPAC resolution comes into play wrt CPIM (and formerly CGPM) definitions. Perhaps the exact definition of VSMOW was different in 2005 when the CPIM made their decree than in 1982 when IUPAC looked at the issue? Wikipedia says VSMOW was created in 1967 as a way of making something more reliable to go by than SMOW, but, it doesn't say if the definition has been adjusted over time (cite note #1 from WP:VSMOW, dated 1995, might be good reading on this, but, I have other things to do right now).