Supplementary comparisons of DC high voltage measuring reference instruments COOMET 449Ru-a08 (COOMET_EM-S7) - Kiselev, Victor; Gromochkova, Elena; Dubrovskaya, Tatiana; Garnacho, Fernando; Kumanova, Ginka; Kikalo, Valery; Kopshin, Vladimir (Metrologia, 2024)