# Calculate Average and Standard Deviation Spectra

To find the average or standard deviation of spectra, use the Statistical Spectra tool in the Process menu.

For each X value of your spectrum, you can find the average or standard deviation of the Y value. This creates a new spectrum.

- Average: Finds the arithmetic mean of the Y value for each data point. If you have taken several measurements of a sample material, you can calculate the average spectrum to reduce the effect of measurement variations. The average spectrum is also useful as a reference spectrum since it may be more representative of a compound than any single measurement.
- Standard Deviation: Finds the standard deviation of the Y values for each data point. By comparing the variance of peaks, you can detect if impurities were introduced during a production process.

You can also use the standard deviation to compare spectra of a standard sample that you measured at different times. This is a useful way to test the repeatability of the measurement.

You can calculate statistical spectra only in the Desktop view of the software. Use the Processing tile to calculate statistical spectra in workflows.

❖ To calculate statistical spectra

- From the Spectral view, select 2 or more spectra to use in the calculation.
- Go to the Process menu and select
**Statistical Spectra**. - Select the calculation you want to perform and the data format to use for the calculation and then select
**Calculate**. The resulting spectrum is added to the Results panel. You can see which spectra were used to generate the new spectrum in the new spectrum's Measurement Information.