So, we did an experiment to find the dissolved oxygen concentration in % over time in a stirred tank reactor at 2 different flow rates and at 3 different agitator speeds. We did not do any repeat measurements, it was just one reading per condition. Now I am confused what sort of error bars I could include on my graph. I have fitted a line of best fit for the data. Error bars are usually standard errors of the mean but no repeats were done and hence I have no mean value to base it on. Should the error bars in this case be uncertainties in the variable arising from measuring instruments. Are there curve fitting error bars I could use here? If yes, what could they be? Btw I am plotting 3 graphs in total. In the first graph, I am plotting three sets of data, each set representing the particular agitator speed, of DO% against time. The first one is for flow rate of 5L/min. The second graph is for flow rate of 10 L/min, and again there are 3 sets of data of DO against time. The 3rd graph is of Mass transfer coefficient*Area (Kla) vs agitator speed. There would be 2 lines on the same graph because each line corresponds to a flow rate condition. I have fitted a best fit line on the first two graphs to calculate the gradient and hence Kla. I think I will put a trendline for Kla vs speed graph too.