I have a .txt file with ten semi-colon separated values on each line. Date and time is the first value, and weight is the eight value. From this data I made a graph, with time as the x-axis and weight in grams as y-axis. I have weight gain by two different sources: one is a linear increasing weight gain from rust, and the other is the weight gain that I’m interested in. How do I make a corrected graph that shows the weight gain, with the linear weight increase from rust removed, if I know the slope?