Euro (EUR) vs. Polish Zloty (PLN) reference exchange rate. Foreign exchange reference rates are published by the European Central Bank. Reference rates are usually updated by 3:00pm CET, based on a regular daily concertation procedure between various central banks across Europe and around the world. This procedure normally takes place at 2:15pm CET. Reference rates are mid-market rates, calculated as averages of the buying and selling rate; they do not necessarily reflect actual transaction rates. Euro foreign exchange reference rates are always quoted using the 'certain' method (i.e EUR 1 = X foreign currency units, where X is the published reference rate).