1. A method of determining a value of a property of a sample with a spectroscopic system, the method comprising: measuring, with a first spectroscopic system, spectra of a first set of at least three different reference targets, each having a known, unique reflectivity spectrum; calibrating the first spectroscopic system based on the spectra of the first set of reference targets measured by the first spectroscopic system; measuring, with the first spectroscopic system, a spectrum of a known reference specimen having a known value of a property; generating a model for determining the property on the first spectroscopic system using the spectrum of the known reference specimen; measuring, with a second spectroscopic system, spectra of a second set of at least three different reference targets, each having a known, unique reflectivity spectrum; calibrating the second spectroscopic system based on the spectra of the second set of reference targets measured by the second spectroscopic system; applying the model to the second spectroscopic system; measuring a spectrum of a sample using the second spectroscopic system; and determining a value of the property of the sample based on the spectrum of the sample measured by the second spectroscopic system using the model.