NAVAIR INSTRUCTION 4120.11 From: Commander, Naval Air ...

NAVAIRINST 4120.11
TABLE 3. Minimum and optimal character heights for various
viewing distances at viewing angles of 16 and 20 minutes of arc.
Viewing Distance
(Inches)
Minimum Character
Height
16 Minutes of Arc
(Inches)
Optimal Character
Height
20 Minutes of Arc
(Inches)
18 0.08 0.11
24 0.11 0.14
30 0.14 0.17
36 0.17 0.21
42 0.20 0.24
48 0.22 0.28
54 0.25 0.31
60 0.28 0.35
66 0.31 0.38
72 0.34 0.42
NOTE: The formula used for the above calculations is:
Character Height = [(Min of Arc x Viewing Distance)/(57.3 x
60)].
7.2.1 . Character font. All titles, headings, callouts and special
characters should be sans-serif font. Narrative text should be
sans-serif font. Table 3 lists the minimum recommended
character heights for various reference viewing distances and
should be used to determine the appropriate character font size.
Unless otherwise specified by the procuring activity, the
minimum reference viewing distance should be 36 inches.
7.2.2 . Character spacing. Character spacing in textual displays
should be no less than 0.1 character height. Between word
spacing for textual displays should be one character width (em
space).
7.2.3 . Line dimensions. Between line spacing for textual display
distances 0.33 of character height exclusive of superscripts and
subscripts and no less than 0.15 character height when
superscripts and subscripts are displayed.
7.2.4 . Text panes. The width of the text pane should range from
30-60 characters per line.
Enclosure (4) 28