Indirect approach for measurement of main physico-chemical parameters of engine oils using optical methodsTsvetelina Georgieva, Eleonora Nedelcheva, Stanislav Penchev, Albena Ivanova-Vasileva and Plamen DaskalovE3S Web Conf., 638 (2025) 03004DOI: https://doi.org/10.1051/e3sconf/202563803004