For each data field a Threshold or Improvement can be set:
The default value None means that this field is ignored, so it can have any value without affecting the build stability. Threshold levels are displayed on the trending graphs.
This sets the message level from which the message total is calculated. Only messages from this level and above are summed to give the message total which is used for the Messages Threshold comparison. Note that Compliance Index thresholds are not affected by this setting.
This is the total number of messages on all levels for all the files in the project. Messages in header files are de-duplicated (they are only counted once and not for each source file the header is included into).
This is the percentage of message groups (a coding standard "rule") for which there are no messages in the project.
This is the mean across all files of the percentage of message groups (a coding standard "rule") for which there are no messages in each file.
A high File Compliance Index and low Project Compliance Index indicates that each file violates only a small number of rules but each file violates a different rule.
If the Compliance Indices are close then each file is violating more or less the same rules.
Note that you can have thresholds set on more than one item - if any of the data fields fall below their threshold then the build will be marked as unstable.