Global filters
Global filters allow you to focus the calculation on a subset of events having certain properties on them. This could for example be events sent from specific countries.
This type of filtering will reduce the complexity of the calculation (less events) and deliver results faster. However the filtering is only allowed on static dimensions (where the value does not change from install and onwards for the player).
Read more about Static Global filters here. Other filtering dimensions (like Build) are available when using the Event Actions controls.
This limitation is due to the calculation requiring all events from a specific player to be included. Only having some of the data would affect the returning user calculation.
Using custom dimensions (Custom01, Custom02, Custom03) in Global filters requires that the value is set before the first SDK initializes and that it is never altered. This will ensure the value being present on all events sent.