A method which has received extensive development work is the “backcalculation” method. This is essentially a mechanistic evaluation of pavement surface deflection basins generated by various pavement deflection devices. Backcalculation is one where measured and calculated surface deflection basins are matched (to within some tolerable error) and the associated layer moduli required to achieve that match are determined. The backcalculation process is usually iterative and normally done with software. An illustration of the backcalculation process is shown in Figure 4.