Citizen 810R

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Calculators: Handheld: Citizen 810R

		Size (approx):	87mm(max) x 150mm x 33mm(max) (w,h,d) Weight 276g including rechargeable batteries
		Power:	6V through 4 x AA size rechargeable battery pack which sits in a battery compartment at the rear but is soldered into circuit. It accepts an adapter/charger (undefined, centre negative) through a socket on the top side two thirds towards the left. The on/off switch is on the left hand side and is three position DC/Off/AC.
		Case:	Two-piece light and dark grey smooth plastic case. The green plastic display filter has a frosted border, is inset and prominently tilted. Below this is a black printed metallic sticker sitting in its own recesses with the brand with model number. A decimal selection and memory switch next to this label has embossed lettering and blue dust stops. The keyboard surround is patterned grey plastic. The large keys are soft touch with a soft metallic click on return.
		Display:	8 digit green VFD, with additional symbol cluster for overflow, negative and memory indication.
		Features:	Standard four functions with percentages and two function switch auto accumulation memory. Additional switch for fixed/floating/financial decimal point modes.
		Age:	1974
		Manufacturer:	Citizen Business Machines Inc., made in Japan, serial number 40332060
		Comments:	Sturdy calculator of the familiar Citizen colour scheme that is equally home as a desktop model or a slight large hand-held. The logic is now archaic with arithmetic (semi-RPN) input but otherwise good recovery and only let down by the pseudo fixed decimal bug. My example's batteries still held a charge! The original cover is soft black plastic with a zip that is full-length right, bottom and 3/4 length left with a rope-like carry strap.

Components:	1 x cpu: Rockwell A1030PC? 7418, (week 18 of 1974), 42 pin staggered DIL, 0.6" width black ceramic with metal cap 1 x 8 digit plus symbol VFD single glass tube round face: Futaba 9-CT-01 4A (January 1974) 17 x transistors 5 x diodes 5 x capacitors 6 x resistors 4 x resistor arrays 1 x transformer 1 x power circuit unit: Fuji MCT 2805 1 x rechargeable battery pack
Boards:	The keyboard assembly sits lose on top of the battery compartment and is attached to the lower main cpu board (T-9CT) via nine strong wires. The whole assembly sits lose inside the case.
Construction:	Held together by internal lugs only, I found the best way was to prize of an edge, at the bottom first, then the bottom and travel up both sides. Push in the grey side as you lever out the rear with a soft blunt instrument to avoid damage. The front will easily lift off, hinging to the right as the switch is fixed to the front.

Logic comments:	(C) is used once to cancel the last number entered and a second time to clear the whole calculator, like a (CE/C) key
	There is automatic constant on multiply and divide only
	Input is in arithmetic (semi-Reverse Polish Notation) mode, to work out 5-3 key in (5)(+)(3)(-)
	Input overflow is suppressed, keying a ninth digit is ignored
	Negative numbers are shown with a "-" in the far right symbol cluster, thereby allowing full eight-digit negative numbers
	Overflow shows the result with a "°" in the far right symbol cluster and is recoverable by using (C)
	Divide by zero shows zero with a "°" in the far right symbol cluster and is recoverable by using (C)
	You can switch between floating [F], financial [A] and fixed four digit decimal mode [4]. Financial input causes (3)(4)(5) to key in as "3.45"
	The memory when switched on is auto-accumulating, i.e. the result of every (=) key is added to memory
	Memory store is indicated by a "_M" in the far right symbol cluster
	Memory overflow shows the result shifted
	It suffers the pseudo fixed decimal bug: key in (1)(+)(.)(0)(0)(0)(+) to give "1.000" which remains a fixed three digit decimal number until you need more digits or use multiply or divide

The image left shows the calculator with the front removed.

You can see the easily recognisable Rockwell IC with the staggered pin configuration. However, the ID plate has been painted over in black ink - did they have an argument !

Loads of transistors crammed together (the little black rectangles and half-circles) for segment and digit driving.

The small blue box near the bottom is a min-board with power supply circuitry.