TM 11-6625-2440-12
Substituting the value of the cosine function (ref d below);
(3) Calculate the frequency by substituting the
the formula becomes F = (80. 28668 X 0.8267398) Hz or
value for sin λ in the equation F = (40.14323 sin λ) Hz.
F = 66. 376194 Hz.
From thumbwheel switch frequency chart (a above),
Record the calculated frequency.
select highest A-switch setting which represents but does
(4) Using the thumbwheel switch frequency
not exceed the frequency 66. 376194 Hz.
chart in a above, determine the correct HEADING AXIS
A-switch setting is 3, representing a frequency of 56. 25
thumbwheel switch setting for the calculated frequency
Hz.
and set thumbwheel switches accordingly.
The
Subtract 56. 25 from 66. 376194 Hz. Remainder is
sequence and procedure for setting the thumbwheel
10.126194.
switches is the same as in b (4) above.
Select highest B-switch setting which represents but
d. Sine and Cosine Interpolation to 0.1 Minute.
does not exceed the frequency remainder from A-switch
To find the sine or cosine of latitude to the nearest 0. 1
setting.
minute, use a natural trigonometric functions table (TM
B-switch setting is 4, representing 9. 375 Hz.
11-684) and proceed as follows:
Subtract 9. 375 from 10. 126194 Hz. Remainder is
(1) In natural trigonometric functions table,
0.751194.
find and record sin or cos of given latitude to nearest
Select highest C-switch setting which represents but
lower minute and nearest higher minute.
does not exceed the frequency remainder from B-switch
(2) Subtract lower value from higher value.
setting.
(3) Multiply difference by number of tenths of
C-switch setting is 2, representing 0. 585938 Hz.
minutes to which latitude is given.
Subtract 0. 585938 from 0. 751194 Hz. Remainder is
(4) Add product to lower of sin value or
0.165256.
subtract product from higher cos value.
Select highest D-switch setting which represents but
does not exceed the frequency remainder from C-switch
Example:
setting.
(a) Find the sin of latitude to nearest 0.1 minute.
D-switch setting is 4, representing 0. 146484 Hz.
Given latitude = 184.2'
Subtract 0. 146484 from 0. 165256 Hz. Remainder is
Sin 184' = 0.31012.
0.018772.
Sin 185' = 0.31040.
Select highest E-switch setting which represents but
(b) Subtract lower value from higher value:
does not exceed the frequency remainder from D-switch
sin 1855'--sin 184' = 0.31040--0.31012= 0. 00028.
setting.
(c) Multiply difference by desired tenths of a
E-switch setting is 4, representing 0. 018311 Hz.
minute:
Subtract 0. 018311 Hz from 0. 018772. Remainder is
0.00028 X 0.2 = 0.000056.
0.000461.
(d) Add product to lower sin value:
Select highest F-switch setting which represents but
0.31012 + 0.000056 = 0.310176.
does not exceed the frequency remainder from E-switch
setting.
NOTE
F-switch setting is 0.
When cos of latitude to nearest
The complete LEVEL AXIS thumbwheel switch setting
0.1minute is being determined, subtract
should be 342440, indicating the assumed latitude of
product from higher cos value.
3414.1".
c. Heading Axis Latitude Correction. The heading
3-6. Self-Test Procedures
axis latitude correction frequency (F) for any earth-
latitude position may be determined by completing the
Operation of the test set can be checked by performing
following:
preliminary operations (a below) and procedures in the
(1) Obtain the earth-latitude position (λ) of the
self-test chart (c below). A stopwatch is required for
test site from the local cognizant authority.
performing tests in the chart. Explanations of self-test
(2) Determine the sin λ to the nearest tenth of
chart column headings are listed in b below.
a minute as described in d below.
3-8
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