The Clegg Impact Soil Tester provides a means for measuring and controlling soil strength and consolidation levels during trench reinstatement. It is also used to confirm uniform compaction over wide areas of ground, identifying poorly compacted areas and ineffective rolling of materials.

The Tester consists of a 4.5 kg compaction hammer operating within a vertical guide tube. When the hammer is released from a fixed height, it falls through the tube and strikes the surface under test, decelerating at a rate determined by the stiffness of the material within the region of impact. A precision accelerometer mounted on the hammer generates an electrical charge which is fed by a cable to a hand-held digital readout unit. The fast microcontroller in the readout scans and filters the signal and registers the deceleration in units of Impact Value (IV). The Impact Value is an indication of soil strength and shows good correlation with results from CBR tests. Data from the Impact Soil Tester can therefore be used in a similar manner to results from CBR tests performed in the laboratory and in the field. The Tester is powered by a single 9V PP3 battery accessible in a pull-out drawer on the side of the readout unit.

The CIST/882 Readout Unit displays readings of Impact Value (IV) and also shows the number of times that the hammer has been dropped during each test operation.