In order to simplify the user interface you can select the property that will be compared with the specified threshold. Basically, three different properties are available:

Total
  Selects the total number of issues in the current build.
New
  Selects the total number of new issues in the current build with respect to the reference build.
Delta
  Selects the difference of the total number of issues of the current build subtracted by the total number of issues in the reference build.

Additionally, you can select to choose all issues, or issues of a given severity only (error, high, normal or low).