Double Majority
There are certain ballot measures that require a double majority. This means that 50 percent of the registered voters in a city must vote on the measure and 50 percent of those votes must be in favor of the measure for it to pass. For example in order to vote for a city to be disincorporated, there must be a double majority for the measure to pass.
In November 2008, voters passed Measure 56, which exempts May and November elections from the double majority requirement.