Calibration Statistics The Calibration Statistics window has Calculate and Finished buttons. First select the appropriate head overlay in the results Overlay window, then select the Calibration Statistics command under the Display menu (the Calibration Statistics command will not be visible unless an overlay of hydraulic head is shown in the Model window). Click on the Calculate button. Graphic Groundwater will then display traditional measures of calibration based on the residual between the target head and the model head. The statistics are based on the hydraulic head for all layers of the model, not just the layer visible on the screen.