Calculation filters determine which incidents to use in computations. The read-only Master Filter file contains a predefined filter for each calculation. MTB (mean time between) calculations determine the mean time between certain events, such as failures or repairs. The differences between MTB calculations are a result of the types of incidents taken into account.

For example, the FRACAS Incidents filter named MTBF Filter is used with the MTBF calculation. The record selection criteria for this filter is:

When an incident is inserted in the FRACAS Incidents table, Chargeable?, Closed?, and Relevant? are cleared by default (which is logically equivalent to FALSE). This means that they are not included in MTBF calculations. If you insert Chargeable?, Closed?, and Relevant? in the Incidents table or on an Incident form, you can select and clear these checkboxes. For an incident to be included in MTBF calculations, all three of these checkboxes must be selected (which is logically equivalent to TRUE).

In the following table, checkmarks indicate the fields used to determine the incidents that are taken into account in the many different MTB calculations. For example, for an incident to be included in MTBUMA calculations, Closed? must be selected. However, the status of Chargeable? and Relevant? does not matter.

If you remove the filter selection by selecting --No Filter--, no filter is applied. This means that all records are used in the calculation. If you want to count every incident, regardless of its open or close status, severity level, or relevance or chargeable status, you do not apply a filter. If desired, administrators can create new filters in the Filter file for the Project to either override or supplement the filters in the Master Filter file. For more information, see Filters.