However, the NAV gets cloudier when looking into other markets. For instance, international markets are not open in the same time zone as U.S. markets, but foreign stock and bond ETFs are still trading on U.S. exchanges. Since the NAV is taken based on the last price at which it was traded, the NAV may not move during normal hours. Consequently, the NAV for international ETFs, along with most commodity and fixed-income funds, may represent a stale number as these markets don’t necessarily trade during normal U.S. market hours.

In the case of Greece, the Athens Stock Exchange has been closed for at least a week, following the June 28 decision by the Systemic Stability Council for a week-long closure of the country’s banks and local stock market, according to ekathimerini. The Greek bourse remains closed Monday.

Consequently, the traded value of GREK has deviated considerably from its NAV – the ETF is currently trading at a much lower value to its constituents due to the underlying market closure. The last time something similar occurred was during the so-called Arab Spring of 2011 when Egyptian markets were shut down for two months, but U.S. investors were still able to trade shares of the Market Vectors Egypt Index ETF (NYSEArca: EGPT).

Nevertheless, GREK ETF investors may still get a general sense of where the ETF is going through indirect means. For instance, Coca-Cola HBC, which makes up 21.4% of GREK, dipped 3.9% over the past week while the National Bank of Greece, which makes up 9.5% of GREK, saw the value of its American Depository Receipts pare recent gains to fall flat for the week.

For more information on ETFs, visit our ETF 101 category.

Max Chen contributed to this article.