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MpNROE CALCULATING MACHINE 



MODELS 


Hand Operated 


LN 









OPERATING INSTRUCTIONS 

MONROE 

CALCULATING MACHINE 

Hand Operated LN Models 



© 

MpNROE 


MONROE CALCULATING MACHINE COMPANY. INC. 

Generol Offices, Orange, New Jersey 




Copyright 1953 

Monroe Calculating Machine Company, Inc. 


Printed in U. S. A. 
1045-S 

September 1958 


FOREWORD 


T HIS BOOKLET describes the operating controls and parts of 
the Monroe Model LN Calculator and gives step by step instruc¬ 
tions on the four basic arithmetic functions; addition, subtraction, 
multiplication and division. 

The directions apply to both the 8 and 10 bank LN type Monroe 
hand operated machines. The former model has an eight column key¬ 
board, eight places in the upper dials, and sixteen places in the 
lower or result dials. The latter, Model LN 200, is equipped with a 
ten column keyboard, ten places in the upper dials, and twenty places 
in the lower dials. The actual operation of these two models is 
exactly the same; the only difference is in their figuring capacities. 










CONTENTS 


Description of Operating Controls and Parts . 9 

Addition and Subtraction. 11 

Multiplication. 12 

Division. 14 

Decimals . 16 

Addition and Subtraction of Decimal Numbers. 17 

Multiplication of Decimal Numbers. 18 

Division of Decimal Numbers. 20 

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MONROE 

CALCULATOR 
Model LN 



Operating Controls 


1. Upper Dials 

2. Lower Dials 

3- Carriage Shift Knob 
4. Clear-out Crank 


5 . Operating Crank 

6. Repeat and Non Repeat Keys 

7. Keyboard Clear Key 

8. Carriage Shift Lever 


8 





MONROE MODEL LN 


Description of Operating Controls ond Parts 


1) Upper Dials The set of dials located in the upper part of the 
moveable carriage is called the upper dials. These dials show the 
quotient (answer) of a division problem in red figures. In multi¬ 
plication, they show the multiplier (number by which you multiply) 
in black figures. 

2) Lower Dials These are the sixteen (or twenty) dials located in 
the lower part of the carriage. The lower dials show the answer in 
addition, subtraction, and multiplication. They show the remainder 
in division. 

3) Carriage Shift Knob This knob, located at the right end of the 
carriage, is for shifting several places at a time. Simply lift up on 
the knob and slide the carriage to the desired position. 

4) Clear-out Crank This is the smaller crank located at the right 
end of the carriage. A forward (clockwise) turn clears the upper 
dials, and a backward (counter-clockwise) turn clears the lower 
dials. 

5) Operating Crank The operating crank is the larger crank located 
on the right side of the machine. This crank is used in all opera¬ 
tions on the machine. The operator should clearly understand what 
is meant by a forward turn and a backward turn of this crank in order 
to follow the instructions in this booklet. 


9 


6) Repeat and Non-repeat Keys When the repeat key (key marked 
"R") is depressed, any figures set on the keyboard remain down until 
cleared by the operator. W'hen the non-repeat key (key above repeat 
key) is depressed, the keyboard clears after each turn of the opera¬ 
ting crank. The repeat key mus/be depressed when performing multi¬ 
plication and division. 

7) Keyboard Clear Key The keyboard keys are cleared in one of 
two ways, either by depressing the large square zero clear button, 
which clears the entire keyboard; or by depressing the individual 
"zero" clear keys at the bottom of each column, which clear keys one 
at a time. 

8) Carriage Shift Lever By a half turn of this lever, located at the 
left front of the machine, the carriage may be shifted to the right or 
left as desired. The operating crank must be in upright, or "neutral" 
position when shifting. 


TO CLEAR THE MONROE MODEL LN 

The operator should always remember to clear the entire machine 
before starting any new work. Complete machine clearance is a 
simple procedure which can be done almost subconsciously. 

To clear keyboard — Depress Keyboard Clear Key 

To clear upper dials - Make a complete forward turn of 
Clear-out Crank 

To clear lower dials - Make a complete backward turn of 
Clear-out Crank 

NOTE: The operating crank must be in upright, or "neutral" 
position when clearing. 


10 


ADDITION AND SUBTRACTION 


Addition and subtraction can be accomplished with the carriage in 
any position but it is suggested that the carriage be placed in posi¬ 
tion "1", that is, as far to the left as possible. 

The most rapid and efficient way to add and subtract is with the 
non-repeat key depressed so the numbers automatically clear from 
the keyboard. 

TO ADD 

Depress Non-repeat key. Clear machine. 


Set on keyboard 
Set on keyboard 
Set on keyboard 
In lower dials 


12 Make one 
23 Make one 
34 Make one 
69 Total 


forward turn of 
forward turn of 
forward turn of 


Operating Crank 
Operating Crank 
Operating Crank 


TO SUBTRACT 


Non-repeat key depressed. Clear machine. 


Set on keyboard 45 Make one forward turn of Operating Crank 
Set on keyboard 15 Make one backward turn of Operating Crank 
In lower dials 30 Answer 


Repeat key addition and subtraction Addition and subtraction can 
be done exactly as above with the repeat key depressed. When this 
is done, the number added or subtracted remains on the keyboard 
after the turn of the operating crank. This saves time when adding 
and subtracting numbers which have one or more digits the same. 
Try it with the following example: 

Depress Repeat key. Clear machine. 


Set on keyboard 

47 

Make a forward turn of 
Operating Crank 

Change keyboard to read 

43 

Make a forward turn of 
Operating Crank 

Change keyboard to read 

-40 

Make a backward turn of 
Operating Crank 

In lower dials 

"50" 

Answer 


11 


MULTIPLICATION 


Multiplication is a series of additions and is a simple process on 
the Monroe Model LN . It is accomplished by setting one figure 
(usually the larger) on the keyboard and "writing" the other figure 
in the upper dials with the operating crank. The repeat key must be 
depressed when doing multiplication. 

Example: 12 x 12 “ 144 

Method: Repeat key depressed. Clear machine. 

Step 1. With the carriage in position "1", set 12 on the extreme 
right of the keyboard. Turn the Operating Crank forward 
2 turns. Note • 

Step 2. With the Carriage Shift Lever, shift the carriage one 
place to the right. Turn the operating Crank forward one 
turn. 

Result: Upper dials 12 

Keyboard 12 

Lower dials 144 (answer) 

This gives a complete and positive check of accuracy. If the correct 
numbers show in the upper dials and keyboard, the answer cannot 
be incorrect. 

• If too large a number is turned into one of the upper dials, it can 

easily be corrected. Simply position the carriage so the carriage 
position arrow points to the incorrect dial and turn the operating 
crank backward until the correct number appears. If the incorrect 
number is too small, turn the crank forward until it is correct. i 

CONSTANT MULTIPLIER 

The above explanation of correcting the upper dials naturally leads 
to the problem where we have to multiply the same number by sev¬ 
eral different numbers. 


12 


In the previous example, we multiplied 12 x 12. Suppose we also 
had to multiply 12 by 31, and 12 by 15. After completing the first 
multiplication, the machine reads as follows: upper dials, 12; key¬ 
board, 12; lower dials, 144. 


It is not necessary to clear the machine. Leave the 12 on the key¬ 
board and simply change the upper dials to the next multiplier. 


Example: 12 x 31 “ 372 

12 x 15 - 180 


Method: Machine reads as stated above. 

Step 1. Clear nothing. Change the 1 in the upper dials to 3 with 
two forward turns of the Operating Crank. 

V . . 

Step 2. Shift carriage one place to the r+ght. Change 2 in the 
upper dials to 1 with one backward turn of Operating 
Crank. 


Result: Upper dials 
Keyboard 
Lower dials 


31 

12 

372 (answer) 


Step 3. In a similar manner, change the upper dials to 15 and 
we have: 


Result: Upper dials 
Keyboard 
Lower dials 


15 

12 

180 (answer) 


This entire operation is extremely simple. It requires no expert 
knowledge, skill or training, and you know your result is absolutely 
accurate because all the figures used are visible in the machine. 

It can be seen from the above that multiplication can be done in 
either direction. As long as the figures on the keyboard and in the 
upper dials are correct, the result in the lower dials will be correct. 


13 


DIVISION 


Division is just as easy and simple as multiplication. As multipli¬ 
cation is a process of repeated additions, accomplished by forward 
turns of the operating crank, so division is a process of continued 
subtractions, and is accomplished by backward turns of the opera¬ 
ting crank. The repeat key must be depressed when doing division. 


Example: 1728 * 12 “ 144 


Method: Repeat key depressed. Clear machine. 

Step I. With the carriage in position "1", set the dividend, 
1728, on the extreme right of the keyboard. Make one 
forward turn of the Operating Crank. Depress the Key¬ 
board Clear Key and turn Clear-out Crank clockwise. 
(This clears the keyboard and clears the "1" out of the 
upper dials.) 


Step 2. Set the divisor, 12, on the right of the keyboard and 
move the carriage two spaces to the right so that the 
divisor, 12, is in direct alignment with 17, the first 
two figures of the dividend in the lower dials. 

NOTE: In division problems, the left hand figure of the 
divisor on the keyboard must always be either 
directly under the left hand figure of the divi¬ 
dend in the lower dials, or beyond it to the left. 

Step 3. Turn the Operating Crank backward until the bell rings. 

Turn the Crank forward one turn. (The red 1 in the 
upper dials is the first digit of the answer.) Shift the 
carriage one place to the left. Turn the Crank backward 
until the bell rings. Turn the Crank forward one turn 
(bell also rings on the one forward turn to warn you not 
to go any farther). 


Step 4. Continue this operation of shifting the carriage one 
place to the left, turning the Crank back until the bell 
rings and turning the Crank forward one turn. 

Result: Lower dials 0 (remainder) 

Upper dials 144 (answer) 


14 



If the operator is turning the crank backward rapidly and goes a 
turn or two past the bell, he should simply turn the crank forward 
until the bell tings, and stop. Listening for these bells makes it 
possible to perform the division without watching the machine. 

PRACTICE PROBLEMS 


1 . 

510 

-5- 15 

— 

34 

2. 

1400 

-5- 25 

= 

56 

3. 

2432 

+ 32 

= 

76 

4. 

1659 

-5- 237 

= 

7 

5. 

1464 

-5- 122 

= 

12 

6. 

4830 

-5- 14 

= 

345 

7. 

928 

-5- 232 

= 

4 

8. 

1160 

* 145 

= 

8 

9. 

1274 

* 98 

- 

13 

10. 

510 

-5- 85 

- 

6 


Note: Be sure to clear the "1” from the upper dials 
and line up the lower dial figure and keyboard 
figure. 


15 


DECIMALS 


\ 


On all calculating machines, fractions are expressed as decimals. 
For example, 1/4 = .25, 5/8 ■ .625, etc. 

The arrangement of the dials and the keyboard on the Monroe 
makes it particularly adaptable to handling calculations involving 
decimal numbers. 

On the Monroe , all decimals can be set for a complete group of 
problems before starting the work, and all the calculations can be 
completed without any resetting of the decimals. The work is done 
entirely around pre-set, fixed decimals. The one simple rule for 
setting decimals on the Monroe is: 

Keyboard decimal + upper dial decimal “ lower dial decimal 

Decimal Markers The keyboard decimal is marked by turning one of 
the small knurled wheels below the keyboard to the right so that the 
yellow decimal marker appears between the proper keyboard columns. 

The upper and lower dials decimals are marked by the gray pointers 
which can be easily positioned to point off the decimal exactly as 
w r ith paper and pencil. To set a decimal at 2 in the dials, simply 
set the marker to the left of the 2 on the slide. 


16 


ADDITION AND SUBTRACTION OF DECIMAL NUMBERS 


To pre-set the decimals for a group of problems involving addition 
and subtraction, examine the numbers in all the problems and de¬ 
termine which has the largest number of decimal places. Set the 
keyboard decimal marker to accommodate this number of decimal 
places. Set the lower dials decimal at the same number. The upper 
dials decimal is at zero (0) and therefore the Monroe rule, as stated 
above holds. 

Following these instructions, what is the correct decimal setting 
for the following problems? 

12.25 
3.333 
10.2 
25.783 

The correct decimal setting is: 

Upper dials 0 

Keyboard 3 

Lower dials 3 

because 3 is the greatest number of decimal places which appears 
in these figures. 

Set these numbers on the keyboard exactly as they are written. The 
figures which appear to the left of the decimal point should be set 
to the left of the keyboard decimal marker, and those which appear 
to the right of the decimal should be set to the right of the keyboard 
decimal marker. Following the instructions for addition and sub¬ 
traction, given on page 11, the result will always be correct. 

PRACTICE PROBLEMS 


152.45 
160.0 
- 75.242 
237.208 


13.00 

36.60 

-44.30 

26.26 

31.56 


31.35 

42.50 

1.46 

23.59 

98.90 


-3.46 

1.56 

- 21.20 

35.45 

12.35 


17 






MULTIPLICATION OF DECIMAL NUMBERS 


Handling decimal numbers in multiplication is also very simple. As 
you remember from the previous instructions, to multiply on the 
Monroe Model LN, you set the larger number on the keyboard and, 
with the operating crank, turn the other number into the upper dials. 
When this is done, the answer appears in the lower dials. 

Therefore, when multiplying decimal numbers, you should set the 
keyboard decimal marker to accommodate the largest number in the 
problem and the upper dials decimal marker to accommodate the 
other number. Then, following the Monroe rule for decimals, add the 
number of decimal places on the keyboard to the number of decimal 
places in the upper dials and set the lower dials decimal marker at 
this number of decimal places. This is exactly how you point off 
the decimal when multiplying by pencil and paper - add the number 
of decimal places in the two numbers and point off this many places 
in the result. All decimal markers should be set before beginning 
any of the work. 

What is the correct decimal setting for the following example? 

20.125 x .425 - 8.553125 

The larger number (20.125) will be set on the keyboard. It has three 
decimal places so the keyboard decimal marker should be set at 3* 
The other number (.425) will be entered in the upper dial, so set the 
upper dials decimal at 3. Add the two (3 + 3 = 6) and set the lower 
dials decimal at 6. Set the decimal markers accordingly and do the 
example following the step by step instructions below. 

Method: Upper dials decimal 3 

Keyboard decimal 3 Repeat key depressed 

Lower dials decimal 6 

Step 1. Set 20.125 on the keyboard (20 to the left of the key¬ 
board decimal marker and .125 to the right). 

Step 2. With the carriage in position "1", turn the Operating 
Crank 5 turns forward. Shift the carriage one place to 
the right. Make 2 forward turns. Shift the carriage to the 
right. Make 4 forward turns. 


18 


Result: Upper dials 
Lower dials 


.425 

8.553125 Answer 


Note that the .425 appears in the upper dial to the right 
of the decimal marker and the lower dials decimal 
marker correctly points off the answer. 


We should always set the decimal for a whole group of problems to 
avoid changing the decimal markers for every problem. To do this 
for a group of multiplication problems, simply find the largest num¬ 
ber of decimal places appearing in the numbers to be set on the 
keyboard. Set the keyboard decimal marker for this number. Find the 
largest number of decimal places to be entered in the upper dials. 
Set the upper dial decimal for this number. Follow the Monroe rule 
and set the lower dials decimal at the sum of these two. Enter all 
figures around these pre-set decimals and the results will all be 
correct. The following example illustrates this. 

24.75 x .35 - 8.6625 

32.5 x .24 - 7.8 

110.333 x 1.4 - 154.4662 

The largest number of decimal places in the numbers which go on 
the keyboard is 3; in numbers which go in the upper dials is 2, and 
therefore, the decimal setting should be: 

Upper dials 2 

Keyboard 3 

Lower dials 5 

Try the above problems and check the given answers to see if you 
are correct. 


19 


DIVISION OF DECIMAL NUMBERS 


In division, as explained in the instructions for simple division, 
both numbers, (dividend and divisor) are set on the keyboard. There¬ 
fore, when working with decimal numbers, we simply examine all 
the numbers to find the largest number of decimal places appearing 
in the whole group of problems at hand,. Set the keyboard decimal at 
this number. To set the upper dials decimal always decide how many 
decimal places are required in the answer and set the decimal marker 
to one more place than this (to permit rounding off). Again, for the 
lower dials decimal, add the keyboard and upper dials decimal and 
set the lower dials decimal at this number. 

Example: 22.868 v 6.7 ** 3*413 (rounded off) 

12.33 -r 4.25 = 2.901 (rounded off) 

5.56 -r .66 *= 8.424 (rounded off) 

Three is the greatest number of decimal places appearing in all the 
numbers in this group of problems. Set the keyboard decimal at 3. 
We require 3 decimal places in the answers, so set the upper dials 
decimal at 4 (3 + 1 =4). Then the lower dials decimal is 7 (3 + 4 =7). 
Step by step instructions for the first problem follows. Try the last 
two by yourself. 

Method: Upper dials 4 

Keyboard 3 Repeat key depressed 

Lower dials 

Step I. Set 22.868 on the keyboard. Shift the carriage so the 
lower dial decimal at 7 is in direct alignment with the 
keyboard decimal at 3- Turn the Operating Crank for¬ 
ward one turn. Make one forward turn of the Clear-out 
Crank to clear 1 from the upper dials. Depress the 
Keyboard Clear Key. 

Step 2. Set 6.7 on the keyboard. Shift the carriage one place to 
the right. (To align the left hand digit in the lower 
dials with the left hand digit on the keyboard). 


20 



Step j. Turn the Operating Crank backward until the bell rings. 

Make one forward turn. Shift the carriage one place to 
the left. 

Step 4. Continue as in Step 3 until the carriage reaches the 
first position. 

Result: Upper dials 3.4131 (or 3.413 rounded off) 

Do the last two problems and check the answers above for accuracy. 


PRACTICE PROBLEMS 


Results are rounded off to two (2) decimal places. 


1. 

128.43 

-5- 29.5 

= 4.35 

2. 

962.99 

-5- 37.3 

= 25.82 

3. 

26.938 

+ 2.45 

= 11.00 

4. 

63.824 

-5- 5.75 

= 11.10 

5. 

16.50 

-5- .573 

= 28.80 


Note: Be sure to line up the lower dials deci¬ 
mal with the keyboard decimal before setting 
the first number in the lower dials. 


21 






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To find the Square Hoot of a number using 
the Monroe Calculating Machine. 

Take the number 3.03 as an example. 

0 

Take out odd numbers from under the first (far left hand) 3 in the 
above number, until the figure 3 is reached (i.e. 1, 3 etc.) this is 
too high, so wind back to previous figure and press the next key 
below the figure 3 i.e. the figure 2 in this case and move the 
carriage to the left one digit and press the odd number key in the 
next row to the right until the figure 9 i3 reached i.e. 21, 23, 25, 
27 , and the number 29 is read. Fow instead of the figure 2 

press down figure 3 and instead of the figure 9, press down the 
figure 1 thus giving the number 31 on the keyboard and then continue 
to take out odd numbers in the right hand line of keys, thus 33, 35, 
now 35 is too high so wind back on the handle to the last figure //w 
the top window which in this case is 1.7, press the key No.4 instead 
of 5 also pressing the key Fo.1 in the next right hand column, and 
move the carriage to the left one digit thus the number 341 appears 
on the keyboard and continue to press down the odd number; keys on the 
right hand column thus 343, 345, 347, until the number 349 is reached 
this is too high, so come back to 348 press down the key Fo.1 on 
the next right hand column thus giving 3481 on the keyboard, move 
the carriage another digit to the left now 1.74 is in red figures in 
the top window, now 3481 on the keyboard is too high, so come back 
to 3480 move up one more digit to the left on the carriage and take 
out odd numbers in the next right hand column. Thus giving 34801, 
34803, 34805, 34807, 34-809 continue to take out odd numbers thus 
34811, 34813, which is too high,come back to 34812 move carriage to 
left one digit and in the top window the number 1.74-06 should appear. 
In the next available right hand column press down the odd number 
keys thus giving 348121, 348123, 348125, 348127, 348129, 348131, 
348133, 34-8135, 34-8137, this last number is too high, so come back 
to 348136 and the number 1.74068 in Red in the top window. Move 
the carriage to the left one more digit continue to take out odd 
numbers in the next right hand column thus giving 3481361, 3481363, 
3481395, 3481367, 34-81369, 3^81371, 3481373, 3481375, 3481377, 

3481379 the last figure here is too high, so wind back one, giving 
the answer to 3*03^ as 1.740689. 

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