The USA IRS publishes a list of yearly exchange rates titled Yearly Average Exchange Rates for Converting Foreign Currencies into U.S. Dollars. As of this writing, the published average value for USDCNY over 2017 is
This came across as odd, so I looked up a chart and marked off the beginning and end of 2017 (vertical blue lines) as well as the published average (horizontal green line):
My question is (only) how the IRS' published average value is determined. The value is provided to three decimal places, which suggests it is calculated somehow. I appreciate if anyone can shed some light on this.