Thanks to all for your input: The output or the result should be a x,y,z diagram with wavelenght, extinction and time as the axes. I’ve uploaded the following files as an example. USB4J009161__0__14-39-30-858.txt (54.8 KB) USB4J009161__1__14-39-30-969.txt (54.9 KB) USB4J009161__2__14-39-31-063.txt (55.4 KB) USB4J009161__3__14-39-31-158.txt (55.5 KB) USB4J009161__4__14-39-31-268.txt (55.0 KB) USB4J009161__5__14-39-31-363.txt (55.1 KB) USB4J009161__6__14-39-31-457.txt (55.1 KB)