@article{Okunev2015procedure,
author={Okunev, D.. and Tulskiy, M.. and Litvinov, I..},
title={Procedure of NDT Instruments Qualification Tests. Classification of Ultrasonic Testing Devices},
journal={NDT World},
publisher={LLC SVEN},
year={2015},
pages={34-37},
volume={18},
issue={4},
}