The traders who work there still handle certain critical processes, particularly the 4 p.m. closing auctions that determine end-of-day prices for thousands of NYSE-listed stocks. The closing prices are used as benchmarks by index funds and ETFs owned by millions of investors, as well as numerous futures and options contracts. Closing auctions have drawn an increasing share of daily trading volume over the past decade, in part because of the rising popularity of ETFs and index funds.