A transmission spectroscopy device for performing plural consecutive sample measurements, the transmission spectroscopy device comprising: a cell having opposing first and second transparent walls (104,106), a separation of the first and second transparent walls defining a size of the cell, the cell being fillable with a sample to be measured, the cell being drainable to remove the sample and replace the sample with air; plumbing for delivering the sample to the cell and for draining the sample from the cell; and a controller configured to operably control the plumbing to fill the cell with the sample and to drain the sample from the cell, the controller further configured to produce a measured absorbance spectrum of the sample by operably controlling a light source configured to provide illumination to the sample and operably receiving at least one signal from a detector configured to detect light transmitted through the sample, thereby determining properties of the sample based on how much light emerges from the sample and on the size of the cell, and to calibrate the transmission spectroscopy device, when the sample is a known substance sample of a known substance, by: producing a measured absorbance spectrum of the known substance sample of the known substance, the measured absorbance spectrum of the known substance sample formed from a ratio of a first emittance scan of the cell to a second emittance scan of the cell, the first emittance scan taken when the cell is filled with the known substance sample, the second emittance scan taken when the cell is air-filled; subtracting a known absorbance spectrum of the known substance from the measured absorbance spectrum of the known substance sample to form a fringe pattern, the fringe pattern being oscillatory in amplitude with respect to inverse wavelength; and determining the size of the cell from a period of the fringe pattern; wherein the controller is further configured to produce a measured absorbance spectrum of the sample for plural consecutive samples, the size of the cell being updated through periodic calibration to account for variation in the size of the cell over time. a cell having opposing first and second transparent walls (104,106), a separation of the first and second transparent walls defining a size of the cell, the cell being fillable with a sample to be measured, the cell being drainable to remove the sample and replace the sample with air; plumbing for delivering the sample to the cell and for draining the sample from the cell; and a controller configured to operably control the plumbing to fill the cell with the sample and to drain the sample from the cell, the controller further configured to produce a measured absorbance spectrum of the sample by operably controlling a light source configured to provide illumination to the sample and operably receiving at least one signal from a detector configured to detect light transmitted through the sample, thereby determining properties of the sample based on how much light emerges from the sample and on the size of the cell, and to calibrate the transmission spectroscopy device, when the sample is a known substance sample of a known substance, by: producing a measured absorbance spectrum of the known substance sample of the known substance, the measured absorbance spectrum of the known substance sample formed from a ratio of a first emittance scan of the cell to a second emittance scan of the cell, the first emittance scan taken when the cell is filled with the known substance sample, the second emittance scan taken when the cell is air-filled; subtracting a known absorbance spectrum of the known substance from the measured absorbance spectrum of the known substance sample to form a fringe pattern, the fringe pattern being oscillatory in amplitude with respect to inverse wavelength; and determining the size of the cell from a period of the fringe pattern; producing a measured absorbance spectrum of the known substance sample of the known substance, the measured absorbance spectrum of the known substance sample formed from a ratio of a first emittance scan of the cell to a second emittance scan of the cell, the first emittance scan taken when the cell is filled with the known substance sample, the second emittance scan taken when the cell is air-filled; subtracting a known absorbance spectrum of the known substance from the measured absorbance spectrum of the known substance sample to form a fringe pattern, the fringe pattern being oscillatory in amplitude with respect to inverse wavelength; and determining the size of the cell from a period of the fringe pattern; wherein the controller is further configured to produce a measured absorbance spectrum of the sample for plural consecutive samples, the size of the cell being updated through periodic calibration to account for variation in the size of the cell over time.