Proper calibration is required.
You can modify any of the values in the top two sections if you wish to experiment with different values. Press the Calculate button in the third section to calculate the equivalent ground concentrations. The Measured field data can be reset to the original values with the Restore data button. Although the values in the Calculate concentrations section can be edited, the changes are ignored and are always over-written with calculated values when the Calculate button is clicked. These values are applicable to 'infinite' sources at ground level.