Calculating a Majority of Pledged Delegates

Will it take 1,990 or 1,991 of the 3,979 pledged Democratic delegates to win on the first ballot?   1,990 is a mathematical majority, as it is clearly greater than the 1,989 remaining (3,979 minus 1,990) and equals 50.0013% of the 3,979 delegates.

However, some media are reporting that the actual number required is 1,991 based on verbal communication from the Democratic National Committee.  The 1,991 is based on a 50% plus one definition. Half of the delegates are 1,989.5, if one is added it is 1,990.5, which rounds up to 1,991.

This may end up being correct, but we're skeptical for several reasons.

• As noted above, 1,990 is a mathematical majority of the available delegates.  Section 7(d) of the 2020 Call for the Democratic National Convention says: "A majority vote of all Convention delegates eligible to vote on the ballot in question shall be required to nominate the presidential candidate."
• There were also an odd number of delegates in 2016.  Contemporaneous news accounts noted that it would take 2,382 of the 4,763 delegates to secure the nomination. 
• The 50% plus one rule runs counter to Robert's Rules of Order, which "in the absence of other provisions...shall govern the conduct of all Democratic Party meetings."

If we see something official from the DNC specifying that 1,991 is correct, we'll update that information on the site.