Decimo International

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Calculators: Handheld: Decimo International


		Size (approx):	83mm (max) x 132mm x 24mm (max) (w,h,d) Weight 142g excluding batteries
		Power:	6.0V DC, 4 x AA size batteries. It does not accept an adapter.
		Case:	Square shaped two-piece case made from matt and gloss black plastic. All the front edges are covered by a wrap-over brushed aluminium panel. There is a large, oversized green plastic display filter that sits flat and very slightly inset. Below this is another metallic panel printed with black text for the brand and model name. The inset keyboard surround is matt black plastic. The round keys are medium travel with a hollow metal sound but work well to this day. A sturdy metal tag is placed on the bottom edge where a black plastic carry strap is fixed.
		Display:	6 digit green VFD display – with an extra symbol cluster to the left for negative and overflow indication. Display is left leading rather than the normal right used today.
		Features:	Standard four function with display shift for up to 12 digit calculations
		Age:	1973
		Manufacturer:	Not mentioned, but mine may be missing the rear sticker. Serial number 96856 on a sticker on the inside of the battery cover.
		Comments:	I'm not sure that the model name is correct as there is no back label on my example. However, this is rather an odd beast. Six digit/display shift calculators were common in the early 1970s but you don't often see one without an adapter. Such an early calculator would have eaten batteries at a high rate. The logic is a bit archaic with extended overflow, no recovery and negative zero bug. The original case is shaped black plastic with a top flap and front popper closing. You have to insert the calculator in upside-down if you wish to leave the carry strap on.

Components:	1 x cpu; Mitsubishi MA8168B 222S, 24 pin DIL, 0.6" width black plastic/ceramic 1 x 6 digit with symbol cluster VFD; single tube round face: Futaba 7-CT-02 3K (October 1973) 1 x transistor 9 x diodes 6 x capacitors 4 x resistors 2 x resistor arrays 1 x transformer
Boards:	The keyboard assembly (1206K) sits on top of the battery compartment and is attached to the main cpu board (1206K-B) below with 9 stiff wires. Very similar to many Decimo models. There is a small piggy-back board with the
Construction:	Front can be gently prized off after using the coin guide at the top. Squeeze the rear of the case sides in to pop the internal lugs. Quite difficult as it is so stiff so be very careful not to damage it.

Logic comments:	The Clear Entry key (CE) is used to clear an input number, and a second clear key (C) to completely reset the calculator
	Overflow on the input of a number is suppressed - but only after you have fed in twelve digits. Keying the seventh digit causes the symbol cluster "left arrow" to show you that there is now more digits in your number. The (<>) key shows you the remaining digits.
	The constant function is automatic on all four functions
	The negative sign is shown in the far left symbol cluster thereby allowing full twelve digit negative numbers.
	Overflow is quite difficult to get to as you can just carry on calculating if you exceed 12 digits. I suspect this is the 10⁴⁹ limit seen on some early Sinclair calculators. When you do eventually overflow the display shows left arrow and all decimal points alight. It is then not recoverable.
	A divide by zero error is shown by a the arrow on the symbol cluster and all decimal points alight, though the former takes a fraction of a second to switch on.. It is not recoverable.
	It suffers the negative zero bug: key in (1)(-)(2)(=) to give "-1" then (+)(1)(=) will give "-0"

	Built like many other Decimo's - but this must have been one of the first like it. Keyboard sits on top of the battery compartment and connects to the main cpu board underneath You can just see the two-symbol cluster on the left of the display tube: a negative sign and right acing arrow. Notice that while there is no adapter socket the board allows for one at the top right.