Flatness tool allows printing of an object following the imperfections of the platen and ensure a snug uniform within the entire print area. To calibrate the tool go to the "Tools" tab and click on Flatness.
At the bottom of the window that appears, enter in the box "Set all Z to" the value "2" and then click on the Set button.
Now click on "Start" in the middle part of the window.
Place a sheet of paper on the floor at the projection of the extruder.
With arrows appeared in the lower arm up to handling the paper placed on the floor. Once the nozzle touches the paper much to put pressure on it but not enough to block it, press the "next" button. Repeat for all measuring points.
Go to the "settings" menu of the program and select the tab "Flatness". Select "Activate". You can change the value "Number of layers for zeroing", indicating the number of layers to which you applied the fix. After this number of layers printing will be performed again. "Number of points" values in X and Y and "Margin" in X and Y depend on the type and model of printer.