The system by default defines quorum to be 50% + 1 voter. You can change the setting to any percentage + 1 that you would like via the slide bar at the top of each quorum monitor screen:
Regardless of ballot item abstentions, any voter who selects to cast their Ballot is included in the Voted Tally for the quorum. If the voter cast a ballot, which may include abstained sections (if your election rules allow for abstain), the ballot will be included in the "Ballots Casts" numbers on the Quorum graph under and stats.
In the above diagrams, the voters ballots can have differing weights (not each ballot = 1). The All Voters is raw number of cast ballots (not weighted, each ballot = 1). The All Voters-Weighted show the cast ballots based on the voter's weight. In the above diagrams:
If you select the See more button on either chart (#1 above), you wil see more details. See below screen capture for the more details.
In #2 above, the details include:
On the summary screen, if you have groups the quorum for each group is displayed as well. You can select the See More button to see details regarding the group quorum.
On the positions and issues screen, the cast ballot numbers include those who select the on ballot options of "Abstain All Positions" or "Abstain Entire Ballot." The Issues abstentions are counted in the same manner.
If you select See More button on the Position tile, you will see the number details but also an Adjust Quorum button that allows you to adjust the quorum for this position (in the above example the Vice President position)
Notice in the above the quorum for all positions are set to 50%+1, but for the Vice President position, we want to set the quorum to 75% +1. Once we tap the Update Quorum button, the quorum will change for only the Vice President position. We can always change it back by tapping the Use Default Quorum button, which will return it to 50%+1 in the above example.
You can change the quorum for any position or proposition / Issue on their respective tabs.