NRFRS
12-97
ROTARY SLIDE RULE
■
C H A R A C T E R I S T I C S
With this rotary bezel type slide rule, a wide
v a r i e t y o f c o m p u t a t i o n s r e q u i r e d b y p i l o t s
a r e p o s s i b l e .
• Ordinary multiplication, division and rule-
o f - t h r e e c a l c u l a t i o n
• C a l c u l a t i o n o f t i m e , s p e e d a n d d i s t a n c e
• Conversion between nautical miles, statute
m i l e s a n d k i l o m e t e r s
■
S C A L E S
T h e r o t a r y s l i d e r u l e c o n s i s t s o f
A )
a dial ruler fixed on the dial and
B )
a r o t a t i n g e x t e r n a l s l i d e r u l e ( r o t a r y
b e z e l ) .
The outer circumference of the rotary bezel
is graduated at an interval of 3 deg. to form
a u t i l i t y b e a r i n g c o m p a s s , a n d t h e i n n e r
c i r c u m f e r e n c e i s p r o v i d e d w i t h a l o g a r i t h -
m i c s c a l e g r a d u a t e d f r o m 1 0 t o 1 0 0 a n d a
d i s t a n c e c o n v e r s i o n s c a l e ( K M , 1 0 0 0 F T ,
N A U T , S T A T ) .
T h e o u t e r c i r c u m f e r e n c e o f t h e f i x e d d i a l
r u l e r i s m a r k e d w i t h t h e s a m e l o g a r i t h m i c
scale (10␣ –␣ 100) as the rotary bezel, and the
inner circumference is graduated with a time
s c a l e .
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O R D I N A R Y C O M P U T A T I O N
[ M u l t i p l i c a t i o n , d i v i s i o n a n d
t h e r u l e - o f - t h r e e c a l c u l a t i o n ]
* A n y v a l u e o n t h e l o g a r i t h m i c s c a l e i s r e l a -
t i v e , f o r e x a m p l e , “ 1 9 ” a s s u m e s a n y v a l u e s
that are the n-th power of 10, multiplied by
itself ... 1.9, 190, 1900 ...
A
M u l t i p l i c a t i o n
B
Division
[ P r o b l e m ] 30 x 40 = ?
[ S o l u t i o n ]
1 )
B r i n g 3 0 o n t h e r o t a r y b e z e l i n l i n e
with 10 on the fixed scale.
2 )
Read the scale on the rotary bezel cor-
responding to 40 on the fixed scale.
It is 12 (= 1.2 x 10
1
).
3 )
C a l c u l a t e t h e n u m b e r o f d i g i t s f o l l o w -
ing the formula in “Hint for calculation
o f e x p o n e n t s ” .
[ A n s w e r ]
1 2 0 0
[ P r o b l e m ] 120
÷
40 = ?
[ S o l u t i o n ]
1 )
B r i n g 1 2 o n t h e r o t a r y b e z e l i n l i n e
with 40 on the fixed scale.
2 )
Read the rotary bezel scale corresponding
to 10 on the fixed scale.
It is 30 (= 3 x 10
1
).
3 )
C a l c u l a t e t h e n u m b e r o f d i g i t s f o l l o w -
ing the formula in “Hint for calculation
o f e x p o n e n t s ” .
[ A n s w e r ]
3
C
Rule-of-three calculation
H i n t f o r c a l c u l a t i o n o f e x p o n e n t s
=
>
=
>
=
>
A n y n u m b e r c a n b e g i v e n b y a n e x p o n e n t i a l
e x p r e s s i o n a s f o l l o w s .
A s s u m e A = a x 10
x
, B = b x 10
y
, and
C = c x 10
z
. (10 > a, b, c ␣ ␣ ␣ 1)
M u l t i p l i c a t i o n :
Then, the product of A and B is expressed
by C (= c x 10
z
).
z = x + y if c ␣ ␣ ␣ a, b
z = x + y + 1 if c < a, b
D i v i s i o n :
The quotient of A/B is expressed by
C (= c x 10
z
).
z = x – y if a ␣ ␣ ␣ ␣ b
z = x – y – 1 if a < b
[ P r o b l e m ] 3 0 / 1 0 = ? / 4 0
[ S o l u t i o n ]
1 )
B r i n g 3 0 o n t h e r o t a r y b e z e l i n l i n e
with 10 on the fixed scale.
2 )
Read the scale on the rotary bezel cor-
responding to 40 on the fixed scale.
The reading is 12 (= 1.2 x 10
1
).
3 )
C a l c u l a t e t h e n u m b e r o f d i g i t s f o l l o w -
ing the formula in “Hint for calculation
o f e x p o n e n t s ” .
[ A n s w e r ]
1 2 0
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C O M P U T A T I O N F O R N A V I G A T I O N
A l l t h e e x a m p l e s h e r e c a n b e c a l c u l a t e d a c -
c o r d i n g t o t h e f o l l o w i n g f o r m u l a :
S P E E D = D I S T A N C E / T I M E
[Calculation of time, speed and distance]
A
Time calculation
[ P r o b l e m ]
G r o u n d s p e e d
:
2 0 0 M P H
D i s t a n c e t o f l y :
1 0 0 m i l e s
Time to fly
:
?
[ S o l u t i o n ]
1 )
A d j u s t 2 0 o n t h e r o t a r y b e z e l t o t h e
time index
★
on the fixed scale.
2 )
R e a d t h e f i x e d s c a l e a t a p o s i t i o n c o r -
responding to 10 on the rotary bezel.
The reading is 30.
3 )
For the purpose of determining the number
of digits, the same rule as with the division
applies. Thus, the answer is 30.
[ A n s w e r ]
3 0 ( m i n u t e s )
★
mark at the 12 o’clock position
B
Speed calculation
[ P r o b l e m ]
G r o u n d s p e e d
:
?
D i s t a n c e t o f l y :
1 0 0 m i l e s
Time to fly
:
30 minutes
[ S o l u t i o n ]
1)
Adjust 10 on the rotary bezel to 30 on
t h e f i x e d s c a l e .
2 )
T h e v a l u e o n t h e r o t a r y b e z e l c o r r e -
sponding to the time index
★
on the fixed
scale is read to be 20.
3 )
For the purpose of determining the number
o f d i g i t s , t h e s a m e r u l e a s w i t h t h e
d i v i s i o n a p p l i e s . T h u s , t h e a n s w e r i s
2 0 0 .
[ A n s w e r ]
2 0 0 M P H
★
mark at the 12 o’clock position
SPORTS
NAU
T.
70
S
TA
T.
80
55
50
45
1:10
1:20
1:30
1:40
1:50
2:00
2:30
3:00
25
25
30
35
40
45
50
55
60
24
24
23
23
22
22
21
21
20
20
19
19
18
18
17
17
16
16
15
15
14
14
12
12
11
1
10
90
80
70
1
4:00
5:00
6:00
7:00
8:00
9:00
3:30
4:30
60
15
30
45
60
75
100
120
SE
150
165
195
210
SW
240
255
W
285
300
NW
330
345
N
05
10
15
20
40
45
50
55
90
10
T i m e i n d e x
( r e f e r e n c e p o i n t f o r
t i m e c o n v e r s i o n )
U t i l i t y b e a r i n g
c o m p a s s s c a l e
L o g a r i t h m i c s c a l e
o n f i x e d s c a l e *
L o g a r i t h m i c s c a l e
o n r o t a r y b e z e l *
A
-
1 )
B
-
2 )
C
-
1 )
A
-
2 )
B
-
1 )
C
-
2 )
