Decimo Vatman Spy

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Calculators: Handheld: Decimo Vatman Spy

		Size (approx):	62mm x 98mm x 20mm (w,h,d) Weight 66g excluding batteries
		Power:	9V DC, 1 x PP3 size battery. It accepts an adapter (undefined) through socket on the bottom side to the far right. The on/off switch is on the left hand side, towards the top.
		Case:	Compact rounded side case made from two pieces of matt black plastic. The front is dominated by a brushed aluminium panel that wraps over the vertical edges. A slightly raised show-through black display escutcheon has the model name printed in silver text. The flat and slightly inset red plastic display filter gives a bright image with limited angle of view. The small keys rattle a bit and are short travel with a positive soft click.
		Display:	8 digit red LED with individual bubble lens and no ninth digit
		Features:	Standard four functions with percentage, counter and total entries.
		Age:	1975/6
		Manufacturer:	No country of origin or manufacturer, just Decimo and the serial number 532381 is on a sticker inside the battery compartment.
		Comments:	Palm-sized compact calculator with an attractive layout and some unusual functions. The logic is quite good and only let down by lack of recovery and seven digit negative numbers. The original case is soft black plastic with square edges and an open top.

Components:	1x cpu: Mostek MK50282N 7545 FF (date code week 45 of 1975), 28 pin DIL, 0.6" width black plastic 1 x 8 digit red LED display unit 8 x transistors: Hitachi C1390 5A (date code January 1975) 0 x diodes 0 x capacitors 9 x resistors
Boards:	The main cpu board sits on top of the keyboard assembly and is joined by 13 strong wires. This board is held in place by two plastic side lugs.
Construction:	The case is held together with internal lugs only so be very careful not cause damage it if you want to open it. The best way I found was to approach one of the side edges, push in the front section and use a non-damaging implement (such as a plastic coffee stirrer) to prize up the front section. The back will eventually lift of but on my example the top edge was the most difficult to lever off. Damage is highly likely so be very careful.

Logic comments:	(C/CE) is used to cancel the last number entered and a second press will clear the whole calculator
	Input overflow is not suppressed, keying in a ninth digit causes an overflow state which is not recoverable
	Negative numbers are represented by a “-“ in the immediate left hand digit but as there is no ninth digit to travel into you are limited to seven digit negative numbers
	There is automatic constant on all four functions
	Overflow shows the result flashing and is not recoverable
	Divide by zero shows flashing zero and is not recoverable
	The percentage key divides the last input number by 100, once only
	The (N) key returns the total count of numbers entered in calculations
	The (I) key increments the current displayed number by one
	No apparent bugs found

	This image with the rear section removed shows the main cpu board sitting on top of the keyboard assembly. You can see at the top the eight transistors used to drive the display digits. At the bottom are the 13 wires to the keyboard and to the bottom left the coloured wires to the adapter socket.