Citizen 831RD Type III

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Calculators: Handheld: Citizen 831RD (type III)

		Size (approx):	86mm(max) x 165mm x 22mm(max) (w,h,d) Weight 206g including batteries, 158g without
		Power:	3V DC, 2 x AA size rechargeable battery pack or disposable battery pack. It accepts an adapter/charger (CTZ-831RD) through a socket on the top side on the far left. It is a 2.5mm plug with centre positive.
		Case:	Made from a two-piece light grey smooth plastic body it is notable for its prominent battery pack in dark grey plastic on the top. The whole pack slides off with batteries intact and is has a near full-width label. The back has an embossed diagram of how to remove the pack. A slightly tilted green display filter gives a bright display. Within the filter there is a recess that houses a silver printed piece of black plastic with the company and model names. The keyboard surround is brushed aluminium with black printed text. The prominent keys are squishy with long travel but work well and the blue and grey colour scheme looks quite nice. Smaller keys are used for the less often used functions.
		Display:	10 digit green VFD, with an additional symbol cluster for negative, memory and error indication.
		Features:	Standard four functions with percentages, change sign, register exchange, square root, squares, reciprocal and four function memory. Additional switch for Floating/1/2/4 decimal point definition and memory summation.
		Age:	1979
		Manufacturer:	Citizen Business Machines Inc., made in Japan, Serial No. 00208688
		Comments:	On the large side for a handheld calculator but the wedge shape makes it easy to hold. It is equally at home on the desktop as well. The dominating battery pack case is odd but helps to keep the whole thing quite slim. The logic is very sound but the lack of overflow recovery a nuisance. Quite a large component count for such a late date. The original case is light tan stippled soft plastic. It has an open top and half-moon cut-outs at the sides with Citizen embossed on the front. There was also a version 831RD and presumably a version II. Very confusing!

Components:	1 x cpu: NEC D1001C W6X079, 28 Pin DIL, 0.6" width 1 x 10 digit VFD with symbol cluster display flat face single tube: NEC FIP 11A6A 9K (October 1979) 2 x transistor 8 x diodes 7 x capacitors 3 x resistors 0 x resistor arrays 1 x transformer 90C 1 x rechargeable battery pack (two permanently connected AA-size) Sony-Eveready 2CH500A 2.4V 500mAH, made in the USA
Boards:	The keyboard assembly (GICO) sits above the main cpu board and is joined via 17 stiff wires.
Construction:	Remove the battery pack by gently squeezing in the front and pulling it up. The side lugs are popped by pressing the rear section in on one side. The front will eventually lift off. Very easy to cause damage so if in doubt don't bother.

Logic comments:	(CE) is used to cancel the last number entered and (C) to clear the whole calculator.
	There is automatic constant on all four functions
	Input overflow is suppressed, inputting a ninth digit is ignored
	Negative numbers are shown with a "-" in the immediate left digit travelling into the far left (ninth) digit thereby allowing full eight-digit negative numbers
	Divide by zero shows "o” in the upper section of the far left (ninth) digit and is not recoverable
	Overflow shows the result with "o" in the left most (ninth) digit and is not recoverable
	The change sign can be used in mid-number entry but is not needed in a lot of calculations as you can use the minus key before multiply and divide.
	Memory store is indicated by an “r” in the upper section of the far left (ninth) digit
	Negative square roots are not allowed but show the result which is unrecoverable

	The scan left shows the rechargeable battery unit that fixes to the top of the calculator. Notice the Sony-Eveready branding and the made in the USA label. To the right is a scan from the top side...		Ah, now we can see where the model "RD" comes from, the R is for the rechargeable pack whilst the D is for the disposable battery pack. The hole to the right is for the AC adapter to connect through.
		The box shown left is 220mm by 97mm and is 32mm deep. It is extra long to accommodate the calculator and the additional battery pack. Printed in blue and black only and has the serial number of the calculator stamped on one end flap.