# Article 2 — Obligation to calculate the ratio of unexecuted orders to transactions **Commission Delegated Regulation (EU) 2017/566 · binding · OJ L 87, 31.3.2017 · dated 18 May 2016 [in force]** *In force · Commission Delegated Regulation (EU) 2017/566, OJ L 87, 31.3.2017 · Checked against EUR-Lex on 26 Oct 2026 · [Official source](https://eur-lex.europa.eu/eli/reg_del/2017/566/oj/eng)* Trading venues shall calculate the ratio of unexecuted orders to transactions effectively entered into the system by each of their members and participants for every financial instrument traded under an electronic continuous auction order book or a quote-driven or a hybrid trading system.