Instrument Classes are collections of manufacturer/model numbers that are similar with respect to function. Defining an Instrument Class is advisable from the standpoint of accumulating sufficient data for interval analysis. Instrument Classes also make ideal groupings for assigning intervals to newly acquired items that can be assigned to a Class.  

Instrument Classes can be created, updated or deleted with the Class Code Builder, which is accessed by first selecting Class-Level Analysis from the Analysis Level menu on the Main Screen and then clicking the Class Builder button.  If no Instrument Classes currently exist, the first screen that will appear is the Create a New Class Code screen for entering a Class Code, a Class Description and Measurement Area (optional). Clicking the OK button returns processing to the Class Code Builder with the new Instrument Class added.  The Create a New Class Code screen can also be activated by clicking the New Class button on the Class Code Builder.  An entire Instrument Class may be deleted by clicking the Delete Class button.

 
A manufacturer/model are added to an Instrument Class by clicking a model number in the Candidate Models List on the Class Code Builder and dragging it to the Member Models List.  A manufacturer/model is removed from an Instrument Class by clicking the class member on the Member Models List and then clicking the Remove Model button.
 
Once an Instrument Class is defined, the data from its member models will be grouped for Class Code Analysis from that point on. If the option to subgroup has been selected as an Analysis Parameter, the analysis will automatically subgroup the class and determine intervals for subgroups as well as for each 
 

During interval analysis, if a class is found to be inhomogeneous, IntervalMAX automatically creates Subclasses or subsets of items in Instrument Classes.  These subclasses are subsets whose service history data have been tested and found to be homogeneous with respect to the rate at which out-of-tolerances occur. The process of creating Subclasses is one in which groupings are created, redefined, recombined, or subdivided until the smallest possible number of homogeneous Subclasses is obtained.  Confidence levels for creating Subclasses and recombining them can be entered in the Subclass Test Confidence Level and Recombine Test Level boxes of the Analysis Parameters Screen.