1. A method for determining at least one physical property of a sample hydrocarbon using spectrometry, said method comprising the steps of: (a) selecting a reference hydrocarbon; (b) selecting a teaching set of hydrocarbons, each having at least one physical property of the at least one physical property to be determined; (c) placing said reference hydrocarbon in a reference cell in thermal contact with a sample cell; (d) placing one of said hydrocarbons from said teaching set into said sample cell; (e) measuring a reference absorption spectrum of said reference hydrocarbon; (f) measuring a teaching absorption spectrum of said hydrocarbon within said sample cell wherein a set of wavelengths used for said measuring is the same as a set used in step (e); (g) combining said reference absorption spectrum and said teaching absorption spectrum to create a teaching adjusted spectrum; (h) computing a plurality of teaching sample values, one for each of a plurality of sample points of said teaching adjusted spectrum; (i) inputting each of said teaching sample values into a multivariate analysis system to build a multivariate calibration model; (j) repeating steps (d) through (i) for each hydrocarbon in said teaching set; (k) placing said reference hydrocarbon in a reference cell in thermal contact with a sample cell containing said unknown-hydrocarbon sample; (l) measuring a test reference absorption spectrum of said reference hydrocarbon in said reference cell, wherein a set of wavelengths used for said measuring is the same as a set used in step (e); (m) measuring a sample absorption spectrum of said unknown hydrocarbon in said sample cell wherein a set of wavelengths used for said measuring is the same as a set used in step (e); (n) combining said test reference absorption spectrum and said sample absorption spectrum to create a test adjusted spectrum; (o) computing a plurality of test sample values, one for each of a plurality of sample points of said second adjusted spectrum; and (p) inputting each of said test sample values into said multivariate analysis system to compare said test sample values to said multivariate calibration model to determine said at least one physical property of said sample hydrocarbon.