Sometimes we accumulate huge amounts of spectra in a CAL file, and most of them is redundant and maybe that not helps to improve the calibration. One thing important when we have a lot of spectra is that we have more when we can select and to fill our hypercube in the best way. The option "Select Samples from a Spectra File" in Win ISI help us to select samples which fill the hypercube with the samples at similar distances between them, so all of them are important in the calculation in the centroid, and there are not groups which makes that the centroid is more closer to them. The number of PCs is also reduced and as we can see comparing these two plots (left: without redundant samples, right: with redundant samples) and maybe we increase the variance explained for the PC terms respect to some constituents in the case we want to develop PC regression. So no discard to use this option to improve the calibrations.