An algorithm was used to differentiate reliably and reproducibly between three regions (before, during, and after crystal growth) by fitting three linear functions to the data and selecting the fits that minimised the sum of their root mean square error. The fits are in Figure . This allowed more information to be extracted at each stage of the crystallisation, and facilitated comparison between the subsequent measurements which were performed under a range of conditions. This highlighted the different behaviour of the peak feature compared to the rest of the spectrum (i.e. the differences between crystalline and liquid phases). Whereas the absorption at 1.6 THz increased after 14 min, when crystallisation occurred, the absorption decreased at lower frequencies. Linear fits were performed before (first region, blue), during (second region, red), and after (third region, purple) crystal growth through the field of view.