Journal article: In September 2018, the French government implemented a suite of measures to reduce wage gaps between women and men. Among these measures, a requirement on all private companies with more than 50 employees to calculate their professional equality index. They must attain a minimum threshold on this index, or face sanctions. We analyse the efficacy of this index in highlighting pay inequality between women and men. After first explaining the rules for calculating the index, we analyse the results for companies in 2020 and compare them with male-female pay inequalities measured using other indicators. We observe that the pay gap indicator as measured by the index tends to minimise the true level of inequality, resulting from the exclusion of certain employees, from the option for companies to declare the index to be incalculable, and the methodologies chosen.