Your CURTA Calculator  
is a highquality precision instrument, fitted with automatic
safety locks to prevent operator's errors. Therefore, to obtain best results
and efficient service from your machine, never handle it roughly or attempt
to force its mechanism. Learning how to operate the CURTA is actually very simple; all you have to do is to follow step by step and in the sequence set out the instructions and exercises that follow. Should your CURTA require servicing or repair, it is essential that you entrust your machine only to an authorized CURTA agency. On no account should you attempt to repair or even to lubricate your CURTA yourself. 

The instructions and exercises herein apply both to CURTA model I (8x6x11 digits) and CURTA model II (11x8x15) digits. These two models being identical but for their capacity, it has been deemed sufficient to represent only CURTA model I on the illustrations.  


How to operate your CURTA 

1  The container  
To open turn the lid toward the left. Remove the machine. When operating hold the machine in your left hand, with thumb and forefinger gripping the upper knurled ring and the base of the machine resting in the palm of your hand (see picture top left). 

2  The clearing lever  
When pulled out as indicated by the blue arrow, the clearing lever is in working position. Before storing the machine in its container, press release button and at the same time push clearing lever backward.  
3  The operating handle  
Turn the handle clockwise only
 it is always locked against backward turns and any attempt to force the
handle to turn backwards may damage the machine. One full turn is complete
when the handle is again checked in its zero stop position. In its
zero stop position the handle can be pulled upward (showing a white or red
sleeve at its base) for subtractive (minus) turns, or pushed down
again in its lower or normal position for additive (plus) turns.
The handle must always be brought into its zero stop position before manipulating
any other parts of the machine.
Exercise Turn the handle several times while it is in its lower or normal position (plus turns) and also pulled out in its upper position (minus turns). To finish don't forget to leave the handle in its zero stop. 

4  The carriage  
is the upper knurled ring of the machine
which you grip with thumb and forefinger (see picture top left). The white
arrow on the front of the machine indicates the positions of the carriage,
which are numbered on its lower edge. To move the carriage from one position to another, make sure the handle is in its zero stop, raise the carriage straight upward, then turn it until the indicator arrow points to the required position and let the carriage snap down into its lower position. 

Exercise Practise moving the carriage first using both hands. As soon as the movement
is familiar, learn to move the carriage only with thumb and forefinger
of your left hand (in which you hold the machine): 

Important: The carriage can be raised only when the
operating handle is in its zero stop.
While the carriage is raised, the operating handle is locked and can only be turned once the carriage has snapped down into its lower position. 

5  The setting knobs  
are numbered at the bottom of the setting register. When pushed right up, they are in their zero position and immediately above each knob the corresponding slot of the setting dial then shows zero. Moving a knob downward, any number from 19 can be set and checked in the corresponding setting dial slot above. When setting a number with several digits, each digit is set with one of the knobs, so that the number desired can be checked by reading it from left to right in the setting dial.  
Exercise
Set the number 149 as follows: With the thumb of the left hand or the forefinger of the right hand pull knob 1 right down until a 9 appears in the dial slot above: With knob 2 set the "4" and with knob 3 the "1". Turn the handle once and make sure you leave in its zero stop. 

6  The counting dials  
are located in a circle around the top of the machine. The black dial is the result or product dial, the white dial the counter quotient dial (see picture top right).  
7  Clearing the dials  
is done with the clearing lever (see 2), which has two stop positions (A and B), located at the
two points where the black and the white dials meet.
To clear both dials raise the carriage with thumb and forefinger of the left hand and with the forefinger of the right hand move the clearing lever steadily around the dials, bringing it back to the initial stop position. 

Important: After clearing the clearing lever must always
be located in one of its two stop positions (A or B). Otherwise the carriage
will not snap down and the operating handle will remain locked. Before starting
the next exercise, please turn the handle several times.
To clear one of the dials only, raise the carriage as previously. then move the clearing lever around the respective dial (black or white) only to its second stop position and let the carriage snap down again. Only one of the dials has been cleared. 

8  The reversing lever  
at the back of the machine has two working positions: the upper is the normal position for al current types of calculations; the lower is to be used only in special cases, particularly for subtraction or division by the substractive method and direct multiplication of quotient in the white dial by a number set on the setting register. 
The 4 arithmetical rulesThe CURTA is ready for use when 
Multiplication 
Multiplication with decimal numbers:
Decimale rule for multiplications:
The number of decimal places in the black dial is equal to the sum of the
decimal places in the setting dial and the white dial.
In this example we have 1 decimal place in the setting dial and 2 in the white
dial. Therefore in the black dial we have
Check: Setting dial 13.6
White dial: 1.15
Answer: black dial 15.640
Shortcut multiplication:
Addition: 
Subtraction 
* Remark: If a check of the number of items added and subtracted is required the reversing lever (see 8 front page) has to be moved into its lower position before doing a minus turn and moved back to its upper position for plus turns.
Addition and subtraction with decimal numbers:
Division: 
Remark: When the dividend is a longer number it will not always be possible to start operating in the highest position of the carriage and one of the next lower positions will have to be chosen so that all the digits of the divisor are transferred into the lefthand part of the black dial with the first plus turn of the handle.
Remainder: When closing the division the remainder can always be determined
as the difference between the given dividend end the number in the black dial.
Here the remainder would be for CURTA model I: 17.2917.28996 = remainder
0.00004;
for CURTA model II: 17.2917.2899996 = remainder 0.0000004.
(Remark: If, for instance, only 3 digits of the quotient had been asked for you could have broken off the calculation when 17.28 was reached in the black dial. The corresponding quotient would have been 14.4 and the remainder 0.01.)
In cases where the remainder is irrelevant it is advisable to work out the
last digit of the quotient to the highest possible accuracy by leaving in the
black dial the number giving the nearest approximation to the required
dividend. Those who are already familiar with calculating machines can equally
well divide by the subtractive method for which they will have to set the reversing
lever (8 front page) into its lower position. The decimal rule remains
unaltered. Division by the subtractive method is however advisable only in cases
where the dividend is already in the lefthand side of the black dial as a result
of some previous operation (f. ex. an addition or multiplication, see CURTA
Computing Examples
Printed in Liechtenstein by BVD Vaduz Copyright CONTINA AG, Vaduz / Liechtenstein


Manufacturer:  
CONTINA  Manufacturing of Office  
and Calculating Machines Ltd.  
Vaduz / Liechtenstein (via Switzerland) 
Last update 21 October, 2002  For suggestions please mail the editors 
Footnotes & References
1  this manual by courtesy of Andries de Man 5/15/1997 
2  This CURTA manual was HTML'ized by Andries
de Man from a (low quality) blackandwhite copy. An attempt was made to
stay as close as possible to the original layout. Thanks to Skip Godfrey
for providing a better copy of the overview image. 
3  See also the US Patents 2,525,352;
2,533,372; 2,544,426; 2,566,835. 
4  For more information, see Rick Furr's CURTA Calculator page. http://www.vcalc.net/cu.htm 