Monroe 8N-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, 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.

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 prevents the keyboard from being cleared.  However, its function is not entirely clear.  With the switch down my machine keeps running until the minus-key is pushed, which inside the machine seems a deliberate way of working.

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 Info Repair information & pictures of internals
RightFront2as.jpg LeftFront-as.jpg Front-as.jpg
P1020055as.jpg P1020054as.jpg

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

Video Assets: adverts, brochures, etc

Serial number:

Build 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.



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