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