Surface Hardness measured by the Clegg Impact Tester has been defined as the ability of a surface to absorb the impact energy created by any object striking that surface. Softer surfaces will absorb a larger percentage of the energy generated upon impact than a harder surface. The Clegg Impact Tester measures Cmax which is a measure of the strength of soil layers. This is achieved by measuring the dynamic rebound of
the soil owing to a standard weight falling from a constant height. Referencefied Proctor hammer with an attached accelerator. They indicated that the unit operates on the principle that
the rate at which the hammer rebounds (soil resistance) is
related to soil strength, bulk density or hardness. The harder the
surface, the higher will be the rebound and so will be the Cmax.
Agronomy research using the CIT has been restricted to evaluating turf root zone firmness on player
performance, with decreases in maximum deceleration as
a result of increases in moisture content. No attempt
has been made to correlate surface hardness with other
soil strength indices.