MIL-DTL-24784 / 21B (SH)
e. Decision blocks. These blocks are used to provide two or more paths resulting from specific
condition related decisions (see figure 21-21). Decision blocks where the exiting line choice is
dependent on a "yes" or "no" decision shall normally have only two exiting lines. These
blocks may have more than two exiting lines if each path is clearly defined by the decision
required to select that path. There shall be only one entry line (either from the top or at the
side) to a decision block. Entry and exiting lines shall not occupy the same side of a decision
block. Exiting lines shall not occupy the top of a decision block. Exiting lines shall be labeled
by decision criteria. Do not include question marks in decision blocks.
f. On-Page connectors. These connectors shall be used to join two ends of a line when it is
inconvenient to draw a single continuous line between two points on a single sheet (see figure
21-22). These connectors shall be shown by a circle enclosing a capital letter. The letter used
in the on-page connectors shall start with "A" and proceed alphabetically on each page. The
same letter shall be used in the starting and ending connectors at both ends of an implied line
of communication. The same letter shall be used in multiple starting connectors when their
respective ending connectors are the same point. Connectors shall have exiting or entry lines
consisting of vectored arrows which indicate that the connector is used as a starting or ending
connector. A single arrowhead with multiple entry lines may be used when required to ensure
clarity (see figure 21-23). The exiting from a starting connector and the entry line to an
ending connector shall show the direction of the corresponding connector and path of the
implied line between.
g. Off-Page connectors. These connectors shall be used to show flow continuity between sheets
of the same figure or of different figures. These connectors shall be shown by an irregular
pentagon enclosing a number and a capital letter (see figure 21-24). The number contained by
the off-page connector shall indicate the destination sheet (for the output connector) and the
origin sheet (for the input connector). The letters used in off-page connectors shall start with
"A" and proceed alphabetically in each figure, using the same letter in the output and input
connectors at each end of an implied line continuation. The same letter shall be used in
multiple output connectors when their respective input connectors are the same point. The
entry line to an output off-page connector shall enter the side of the connector opposite the
point. The exiting line from an input off-page connector shall leave from the point of the
connector. When off-page connectors are used to show flow continuity between figures, the
figure number of the corresponding connector location shall be shown outside each off-page
connector symbol (see figure 21-25). If more than one of the output connectors is located on
another figure, two or more input connectors shall be placed at the entry point so that figure
numbers of all output connectors are shown (see figure 21-25).
h. Arrowheads. Arrowheads shall be used to indicate the direction of flow. All block or
connector entry lines shall have arrowheads. Arrowheads shall be used at all line intersections
to clearly show direction of flow (see figure 21-26).
i. Line intersections. Lines shall not cross except when an intersection is intended. On-page
connectors shall be employed to prevent line crossings where intersections are not intended
(see figure 21-26).
3.5.1.3 FCDs. An FCD shows in symbolic form the interrelationship of the circuits required to
perform a function. The FCD consists of symbols representing circuit modules and electrical
parts complete with physical location and interconnection information. FCDs shall be prepared
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