This alumina spectrum has a region where HyperLab fitted a background curve (2nd order member of the back­ground polynomial), and comple­tely eliminated the slope (1st order member). If you are curious if the fitted curve is necessary, or it may be replaced by a slope, follow the steps below:

When you manually modify a parameter of the fitted region (and change to another editor field), HyperLab automatically displays the new model with a different color scheme. This way you can immediately check the new model. This is, however, only a visual representation, and the entered data is not used elsewhere until you click one of the Set or Set & fit buttons.

As a new fit is required now, the Set & fit button should be clicked, therefore the manually set values are used only as an initial estimate for the fit.

After the fit, the new model is displayed with a background slope instead of a curve. Chi-squared changed from 1.8 to 4.3, so in this case the experiment showed that the slope is a worse parameter to fit the background than the curve.

Click Undo button to restore the previous fit now.