Manufacturer: BUSICOM
Model: 121DK
AKA: exec, 121-DK
Year: 1972
Display: Tubes (12)
Circuits: LSI Chipset MOSTEK: MK6018, MK6019
Dimensions: 242x161x58 mm
Power type: AC
Origin: Japan
S/N: 30QB142057
Owner: DEVIDTS Serge

 

Feature  

Description 

Case:  

Plastic

Color case:  

Beige

Color keyboard:  

Black

Weight:  

1100 g

Voltage selection:  

No

Adapter:  

No

Power consumption:  

3.5 W

Working condition:  

0 to 40 degrees C

Printed Circuit Boards (PCB's):  

2

Memories:  

1

Memories indication:  

Via 'Memory' Neon bulb above display

Prog. steps:  

N/A

Decimal point handling:  

Via Switch on keyboard

Rounding:  

Via Switch on keyboard

Calculation overflow indication:  

Via 'Overflow' Neon bulb above display

Input overflow indication:  

Via 'Overflow' Neon bulb above display

Divide by Zero indication:  

Via 'Overflow' Neon bulb above display

Negative value indication:  

Via 'Negative' Neon bulb above display

Constant function:  

Via [=]

Calculation speed:  

 

Auto Power-off:  

No

Display details:  

 

Printer:  

N/A 

Extra features/remarks:  

When overflow occurs and is cleared, the process, constant and memory contents are retained. 
Unnecessary 0 digits ahead of the numerical display are suppresed.
Setting up the power switch to ON, auto open the display hood, closing the display hood turns off the machine.
The carrying handle is easily slid out for carrying and fits neatly under the machine when in closed position.
Working register capacity: 3 words (1 word = 12 digits + sign)
Memory capacity: 1 word

Initial price:  

 

Overall quality rate (1-10):  

8

OEM copy of:  

 

Other sources of info:  

LACOSTE Robert, TECLAS

Advertisements/Publications:  

Compact Portable Office Calculator...

 

Key / Switch

Description 

EX  

Reverse calculation, the first and de second factors/arguments are exchanged,
(see: Swapping Operands)

CM  

Clear Memory

RM  

Recall Memory

CE  

Clear Entry

C  

Clear

0 to 9  

Numeral keys

.  

Decimal point key

X  

Multiplication key

(division)  

Division key

+  

Addition key

-  

Subtraction key

M (white)  

Memory key:
Adds displayed value to the memory register

M (red)  

Memory key:
Subtracts displayed value from the memory register

=  

Triggers the desired result

9-6-5-4-3-2-1-0  

Decimal selector:
Presets the number of decimal places in the answer
(see:
Decimal point handling and Rounding)

N 5/4  

Round mode Switch, (see: Decimal point handling and Rounding)

M+-  

Memory mode Switch (see examples)

 

Example

Operation

Display Result / remark

Addition and subtraction:
1.23
+9.872-56.78

 

 
[Decimal Point switch]
=3
[C]
1.23 [+] 9.872 [+] 56.78 [-] 


(3 decimals)
(Clear)

-45.678

Multiplication:
2
x5.144x12

 

 
[Decimal Point switch]
=3
[Rounding switch]=N
2 [x] 5.144 [x] 12 [=] 


(3 decimals)
(No rounding)

123.456

Division:
17780
/4/360

 

 
[Decimal Point switch]
=2
[Rounding switch]=5/4
17780 [(division)] 4 [(division)] 360 [=] 


(2 decimals)
(rounding)

12.35
Raising Power (Constant):
3
³


[Decimal Point switch]
=0
3 [x] [=] [=]

(No decimals)
27

Total calculation:
(12x3)+(45x6)+(78x9)


[Decimal Point switch]
=3
[Memory switch]=M+-(double underlined)
12 [x] 3 [M] 45 [x] 6 [M] 78 [x] 9 [M] [RM]


(3 decimals)
(Memory addition mode)

1008

 

 

Display ^

 

 

Swicthes on keyboard ^

 

 

Internals ^

 

 

Internals ^

 

 

NCM (Nippon Calculator Machine Corp.) on bottom of PCB ^

 

 

MicroSwitch: smart solution to power up by opening the display deck ^

 

 

No LEDs, but small Nenon bulbs in 1972 ^

 

 

 

Handle ^

 

 

Label on top ^

 

 

Label on bottom ^

 

 

NCM (Nippon Calculator Machine Corp.) on bottom ^