Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Parpp807-at-aol-dot-com> Also degrees Kelvin which is the absolute scale and based on the extrapolation of the volume expansion of an ideal gas: V / T = V' / T' 0 degrees K = - 273 degrees C 0 degrees C = 273 degrees K Helium liquifies at 4 degrees Kelvin. (usually) :-)) Ralph Zekelman