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Calculators: Decimo Vatman Mini Office III (3)

Decimo Vatman Mini Office III 3, (c) Emil Dudek 2011

(c) Emil Dudek 2011

Size (approx):

150mm x 170mm x 42mm (max) (w,h,d)
Weight 310g excluding batteries


3.0V DC using 2 x D size batteries.  It accepts an adaptor (3V, 0.5W, which means it must have been quite heavy on batteries) through a socket on the top edge to the far right (3V centre-negative worked fine).
Case: The case is formed from a two piece matte black and cream grey design.  The top area is raised in order to accommodate the batteries and has some lines that are fake cooling vents. The blue plastic display filter is angled at 45 degrees and gives a high contrast and easily viewed display.  The keyboard area is printed with black text for the switch labels and model name.  The good-sized keys have a good travel, positive click and are very easy to use.  To the right of the model name is evidence (less fading) of a past sticker that may have been a Decimo logo.

10 digit blue VFD with an additional symbol cluster for negative, memory and error indication.  

Features: Standard four functions with percentage and delta percentage, register exchange, grand total, number of items in the chain and four function memory.  Switch fixed decimal point, switch constant and semi-RPN logic.
Age: 1986
Manufacturer: Decimo, made in Taiwan, serial number 88020764


Compact desktop calculator that is well built.  The functions tend to imply it was aimed at the FD's desk.  The logic is quite solid and only let down by the lack of recovery and unflagged memory overflow.  Quite a lot of components for this late age - mostly devoted to driving the display.

Components: 1 x cpu: Texas Instruments TMC1073BNL MBS8618 Philippines, 28 pin DIL, black plastic, 0.3" width
1 x 10 digit blue plus symbol cluster VFD; single glass unit flat fronted 
2 x transistors
5 x diodes
6 x capacitors
13 x resistors
2 x resistor arrays
1 x transformer
Boards: The main board (Z5604441) sits on the rear section and is fixed by two screws and two plastic studs.  The keyboard board is attached to the front via 12 screws.  They are joined by a 13-way ribbon cable, 11 of which are used.  
Construction: Remove the two small screws from inside the battery compartment and the front will lift away easily, hinging at the bottom.

Logic comments: (CE) cancels an incorrect numerical entry, whilst (C) clears the calculator
Input overflow is suppressed, keying an eleventh digit is ignored
There is switched constant (IN) on multiply and divide only
Negative numbers are shown by a minus in the far left (eleventh) digit thereby allowing full ten digit negative numbers
Overflow shows zero with "<-" in the far left (eleventh) digit and is not recoverable
Divide by zero results in zero and an "<-" in the far left (eleventh) digit and is not recoverable
(GPM) returns the results of a  total chain
(ITM) returns the number of items in a chain
Negative square roots are not allowed and show the result with an error flag which is not recoverable
Memory store is indicated by a small "M" in the fare left (eleventh digit)
Overflow in memory is not flagged and retains the shifted result
There is a switch for floating or two digit (rounded up/down) decimal points
Semi-Reverse Polish Notation takes a little while to get used to; to do 9-5 key in (9)(+=)(5)(-=) to give "4"
No bugs found