and the necessary assemblies, subassemblies, and parts
connected or associated together to perform an opera-
tional function.
Reference designations are assigned beginning
with the unit and continuing down to the lowest level
(parts). Units are assigned a number beginning with 1
and continuing with consecutive numbers for all units
of the set. This number is the complete reference desig-
nation for the unit. If there is only one unit, the unit
number is omitted.
Assemblies and subassemblies are assigned refer-
ence designations consisting of the unit number that
identifies the unit of which the assembly or subassem-
bly is a part, the letter A indicating an assembly or
subassembly, and a number identifying the specific
assembly or subassembly as shown in figure 6-17.
Parts are assigned reference designations that
consist of the unit and assembly or subassembly desig-
nation, plus a letter or letters identifying the class to
which the part belongs (as in the block numbering
system), and a number identifying the specific part.
For each additional subassembly, an additional
letter A and number are added to the part reference
designation. For example, if the resistor shown in
figure 6-16 is the number 1 resistor in the sub-
assembly, its complete reference designation would
be 4A13A5AlRl. This number identifies the number
1 resistor on the number card of rack number 5 in
assembly 13 of unit 4. On electronic diagrams, the
usual procedure is to use partial (abbreviated)
reference designations. In this procedure, only the
letter and number identifying the part is shown on the
part itself, while the reference designation prefix
appears at some other place on the diagram as shown
in figure 6-14. For the complete reference designa-
tion, the designation prefix precedes the partial
designation.
Interconnection Diagrams
Interconnection diagrams show the cabling be-
tween electronic units and how the units are inter-
connected (fig. 6-18). All terminal boards are assigned
reference designations according to the unit numbering
method described previously. Individual terminals on
the terminal boards are assigned letters and/or numbers
according to Standard Terminal Designations for
Electronic Equipment, NAVSHIPS 0967-146-0010.
Figure 6-17.—Application of reference designations using unit numbering methods.
6-18
