Monroe 8N-1-213


The Monroe 8N-213 is a very luxury machine, equipped with many functions easing particular kinds of calculations.  There is a sophisticated back-transfer mechanism from result register to multiplier register, the upper register (counter) consists of two parts which can be cleared separately, the multiplier register can be set to multiply with a constant, etc.  To efficiently use these and other functions required a skilled operator.  Some help existed in the form of publications like:  Machine Methods for Civil Engineering Calculations  and Some shortcut’ Statistical Methods by Monroe.  For links to both documents see the Assets Page).  

The  second publication mentions the CAA10 as a target. However, it fits the 8N-213 well as it is very similar to the CAA-10-3s which was sold as a statistical version of the CAA-10.  The 3s like the 8N is equiped with an extra counter register in the upper left of the carriage.

The internal construction is complex as well.  It looks like being gradually extended without ever carefully  redesigning  the control mechanism.

This particular machine has a square switch. Without the switch the operator can prevent the keyboard from being cleared by keeping the EnterMult button pushed down until the machine stops.  The switch was supposed to form a more straight forward way to prevent the keyboard from being cleared.  

The bottom label shows the Litton Industries logo. Litton acquired the Monroe Calculating Machine Company in 1958. So I guess that this machine was produced after 1958.



Enter a number and hit the “+” or the “-” key.


Enter the 1ste number,  then push Enter Multiplier

Enter the 2nd number,  then push  Clear/Mult (or AccMult or NegMult)


Enter the 1st number, push ‘ENTER DIVD’

Enter the 2nd number, push ‘DIV’  and  ‘Upper’ and ‘Lower’.  By pushing the three buttons together the  registers are cleared before the dividend is set into the Lower Register.

Function of  keys, switches etc

Calculator InfoRepair information & pictures of internals
Monroe 8N-1-213Monroe 8N-1-213Monroe 8N-1-213
Monroe 8N-1-213Monroe 8N-1-213

Although the identification on the bottom marks this machine as 8N-213, the extra switch above the lock-switch suggests it is an 8N-1-213.  

The extra switch supports automatic squaring.  Monroe advertised this machine as particularly suitable for statistical applications.

See Monroe-ca on the assets page.

Click to view a full size picture (opens in a new tab)

Video Assets: adverts, brochures, etc

Serial number:

Built in:


Rotation speed:


Production until:


B 214992

> 1958

Addition, Subtraction, Fully automatic  Multiplication and  Division

635 additions or subtractions per min.  (This machine set to 540)



Approx. DM 4000 in 1964 (was ca. 5000 in 1958) (source: Büromaschinen Lexicon)