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Currently more and more use is being made of the acoustic-emission (AE) method for nondestructive quality inspections of products. That the achievements in this field are substantial is evident from the first-generation measuring facilities (AVN-IM, BF-I, and NI-I) and the new measuring facilities (AVN-2, SA-30 etc.) on exhibition at a show as well as from the basic technical characteristics which are not inferior to those of the well-known instruments from the "Donegan-lndevco" company (USA).

1. The operational documentation, methods, and equipment for checking thickness gauges do not ensure unity of measurement for gauges types MIP-10 and MT-20N. 2. To ensure the unity of measurement of these instruments it is advisable to replace individual standards representing different thicknesses with a smoothly variable air gap. This would enable us to determine important metrological characteristics for all parts of the scale on each range of the instrument. This would enable the many factors influencing the accuracy to be correctly assessed. 3. The instrument need only be checked twice for each range: once as the thickness is increased and once as it is reduced again. 4. The air gap can be used for checking thickness gauges for dielectric coatings on ferromagnetic electrically conducting substrates if their applicability is not limited by the properties of the coating. 5. When a thickness gauge is being calibrated by the use of the air gap, the pressure of the primary transducer on the substrate of the sample or product should be taken into account. 6. The air gap can also be used for adjusting thickness gauges under field conditions.