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Calculators: Desktop: Decimo Vatman Office Deluxe

(c) Emil Dudek 2011

Size (approx):

185mm x 232mm x 65(max)mm (w,h,d)
Weight 996g excluding cable and plug


Mains (240V 50/60Hz, 3.0W) power only through an IEC320/IEC60320-C13 three-way mains cable (computer/kettle type).
Display: 12+symbol digit green VFD: the symbols (to the far left) are used for memory, error and negative indication. 
Features: Standard four functions with selectable floating/fixed decimal modes, switched rounding modes, switch auto-accumulator, switched constant, four function memory, register exchange, percentages, square root and change sign. Semi-RPN logic.
Age: 1978
Manufacturer: Decimo, made in Japan, serial number 80702716.


A sturdy, large desktop from the later 70s which has a few extra useful functions.  The logic is poor with input overflow, no recovery lack of summation on addition/subtraction, strange financial mode input display and negative square roots.

Case and Design: Of three-piece construction made from textured light cream and dark grey plastic, which is quite solid.  The top of the case has a sophisticated cooling grid to keep the dust out.  A heavily inset and tilted green plastic display filter gives a bright and high contrast display.  The upper area has a black printed metallic sticker in its own recess with the model name.

Keys and Switches: The keys in red, blue, cream and black look a bit of a jumble. They are  long travel with a chunky hollow-sounding clunk on pressing and return. The function switches have raised letter that shows no evidence of ever being highlighted, so they are rather difficult to read. The on/off switch is situated on the left hand side, nearly at the top.
Construction: Remove the four screws from the rear, flip the calculator over, remove the small knob from the long decimal mode switch and the front will easily lift off.
Boards: The whole calculator assembly sits in the rear section.  The sturdy metal keyboard assembly sits on top of the main board and is held in place by plastic brackets. It is joined to the main board by a 17-way ribbon cable and an earth wire.  This can be gently lifted away by sliding up and off.  The main board is attached to the rear with four screws, two of which also fix the metal brackets for the display. A transformer and fuse holder have their own metal bracket mounting.
Components: 1 x cpu: NEC D1221C  K6Y146, 42 pin DIL, 0.6" width black plastic
1 x 12 digit + symbol green VFD display, single tube flat glass face Futaba 13-MT-26 8F (June 1978)
1 x transistors
7 x diodes
7 x capacitors
4 x resistors
1 x resistor arrays
1 x fuse
1 x mains transformer (EPS-6E 88-H) (August 1978)

Logic comments: (C) is used to clear the calculator and (CE) as a Clear Entry function
Input overflow is not suppressed: keying a thirteenth digit results in an overflow that is not recoverable
Negative numbers are shown with a minus in the far left (symbol cluster) digit thereby allowing full twelve-digit negative numbers
There is switched (K) constant for divide and multiply only
Fixed decimal modes are selected by a multi-position switch for 0, 1,2,3,4,6  or A.  The latter gives financial input, but rather worrying that this is not displayed during number entry i.e. entering (2)(3)(4) is shown as "234" but is actually "2.34"
There is a rounding switch for round down (v) and round (5/4)
The logic is semi-RPN (Reverse Polish Notation) to do 2-3 key in (2)(+=)(3)(-=)
Negative square roots are allowed and result in a negative number
The change sign key (+/-) can only be used at the end of number input
Divide by zero shows "0."  and "E in the far left symbol cluster and is not recoverable
Overflow shows "0."  and "E in the far left symbol cluster and is not recoverable
The (EX) keys allows to to swap primary and secondary registers
Memory storage is indicated by an "M" in the far left symbol cluster
There is switched memory auto-accumulation mode  "S" (sigma), which only accumulated results from a multiply or divide
Overflow in memory is flagged, is recoverable using (C) and maintains the original number
No bugs found