Set up your spectrometer to collect a full absorbance spectrum with a computer and Logger Pro 3. Follow these steps to prepare the column of % transmittance data:
1) Open the Data menu and choose New Calculated Column.
2) (Optional) Name the new column % transmittance, and use %T as the short name.
3) In the Equation box, type in: 100/10^(Absorbance)
[Note: to accurately enter “Absorbance” in the equation field, simply click the Variables (Columns) button and choose Absorbance. Close the parentheses.]
5) Click Done.

Next, set up your graph to plot both absorbance and % transmittance on the same graph. Follow these steps:
1) Place the cursor anywhere on the graph itself and double click. A new dialog box will appear.
2) Click the Axes Options tab.
3) Check the box next to “Right Y-axis”.
4) Check the box next to the column of % transmittance data.
5) Click Done.

Your graph will be scaled so that the absorbance data uses the left-hand Y-axis and the %T data uses the right-hand Y-axis. In addition, the plots are color coded.