Nenkov, Dimiter. “Bulgarian SOFIX Levels in 2017 According to The “Price-to-Sales” and ‘Enterprise Value-to-Sales’ Ratios”. Finance, Accounting and Business Analysis (FABA), vol. 1, no. 1, Feb. 2019, pp. 33-52, http://faba.bg/index.php/faba/article/view/4.