Biological and chemical assays use calibration curves to establish the concentration of a substance, which is based upon a series of standard samples using a linear regression analysis to determine accuracy. The researcher selects a set of concentrations to serve as the X variable in an X-Y graph. The selected concentrations are often on a logarithmic or exponential scale to provide standards. The solutions then run through the equipment, giving a set of Y outputs that when plotted against the X variables create a calibration curve. Once a calibration curve is established, future samples of unknown concentrations can be plotted using the Y output to determine the initial X variable, which is the concentration of the solution.

Run a set of known X variables through the equipment to produce a series of Y outputs.

Open Microsoft Excel. In cell A1 type "concentration." In cell B1 type "output" or the appropriate unit of measure for your experiment.

Enter experimental concentrations for the X variable in column A, starting at A2.

Enter experimental outputs for the Y variable in column B, starting at B2

Highlight entire data set.

Click the "Insert" ribbon.

Click the "Scatter" button and select the "Scatter plot with markers and straight lines." The graph should now appear and the Excel ribbon should default to design view.

Click on the graph. In the Design ribbon under "Chart layouts," select "Layout 9." The calibration curve is complete. A y=mx+b equation will appear in the graph along with the R2 value.

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X and Y axis labels can be changed to provide more detail about the sample. Other design features such as adding title, changing graph colour and text size can be found in the Design ribbon.