The database is arranged as a hierarchy. For example, the value of a Level-3 equipment category is equal to the sum of its Level-4 subcategories.  A category's level can be determined by the number of non-zero digits.  For example TELECOMMUNICATION (521000) is a Level-3 category.

5-2-0-0-0-0 COMMUNICATION                    

5-2-1-0-0-0 TELECOMMUNICATION             

5-2-1-1-0-0 CENTR OFF SWITCHING           

5-2-1-1-1-0 CLASS 1-2-3                             

5-2-1-1-1-1 ANALOG                                  

5-2-1-1-1-2 DIGITAL                                  

5-2-1-1-2-0 CLASS 4-5                                

5-2-1-1-2-1 ANALOG                                

5-2-1-1-2-2 DIGITAL                                

5-2-1-1-3-0 CELLULAR/PACKET                

5-2-1-1-9-0 OTHER CENTRAL OFF             

5-2-1-2-0-0 TRANSMISSION                       

5-2-1-2-1-0 CARRIER                                

5-2-1-2-2-0 REPEATER

5-2-1-2-9-0 OTHER TRANSMISSION

5-2-1-2-9-1 VOICE FREQUENCIES

5-2-1-2-9-2 FIBER OPTIC

5-2-1-2-9-9 OTHER EQUIPMENT

5-2-2-0-0-0 RADIO COMMUNICATION

5-2-2-1-0-0 AIRBORNE

5-2-2-3-0-0 LAND MOBILE

5-2-2-3-1-0 CELLULAR TELEPHONE

5-2-2-3-9-0 OTHER LAND MOBILE

5-2-2-4-0-0 AMATEUR RADIO

5-2-2-5-0-0 CITIZEN BAND

5-2-2-6-0-0 FIXED STATION

5-2-2-6-1-0 CELLULAR FIXED STATION

5-2-2-6-9-0 OTHER FIXED STATION

5-2-2-9-0-0 OTHER RADIO COMM

5-2-3-0-0-0 MICROWAVE

5-2-3-1-0-0 TERRESTRIAL

5-2-3-2-0-0 SATELLITE

5-2-3-2-1-0 EARTH STATION

5-2-3-2-2-0 SPACE SEGMENT

5-2-5-0-0-0 NAVIGATION

5-2-6-0-0-0 BROADCAST

5-2-6-1-0-0 AUDIO

5-2-6-2-0-0 VIDEO

5-2-6-3-0-0 CATV

5-2-6-9-0-0 OTHER

5-2-8-0-0-0 END USER EQUIPMENT

5-2-8-1-0-0 SWITCHING

5-2-8-1-1-0 PABX

5-2-8-1-9-0 OTHER SWITCHING

5-2-8-3-0-0 VOICE

5-2-8-3-1-0 TELEPHONE SET

5-2-8-3-9-0 OTHER VOICE

5-2-8-3-9-1 VOICE MAIL

5-2-8-3-9-2 VOICE RESPONSE

5-2-8-3-9-3 OTHER CALL PROCESSING

5-2-8-3-9-4 PHONE ATTACHMENT

5-2-8-4-0-0 IMAGE/MESSAGE

5-2-8-4-1-0 FACSIMILE

5-2-8-5-0-0 VIDEO

5-2-8-6-0-0 TELEMETRY

5-2-8-9-0-0 OTHER END USER

5-2-9-0-0-0 OTHER COMMUNICATION