Casio Memory-8A CD-813

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Calculators: Handheld: Casio Memory-8A (aka CD-813)

		Size (approx):	75mm x 135mm x 22mm (w x h x d) Weight 130g not including batteries.
		Power:	3.0V DC using 2 x AA size batteries. It accepts an adapter (AD-2S 3V 0.2W) through a socket on the top side to the far left. The on/off switch is on the left side by the Casio logo.
		Case:	The case is three-piece smooth plastic with a white base and black and white front. A white, blue and black printed label sits in its own recess on the top panel. The neutral display filter is flat and slightly recessed and gives a clean bright image. The typical Casio keys are squishy but work well. They keys are surrounded by a brushed aluminium panel which sits in its own recess with black plastic escutcheons for each key. There is a front switch for floating / 2 decimal rounded display.
		Display:	8 digit blue VFD with no ninth digit
		Features:	Standard four functions with percentages, square root and three function memory. Floating point and two decimal point modes.
		Age:	1976
		Manufacturer:	Casio Computer Company Ltd, made in Japan. Serial number 0987265 on sticker inside the battery compartment, with another on the compartment cover 6414422.
		Comments:	Solid slab shaped calculator that is slightly different from the normal Casio design but maintains a lot of the familiar features. The logic is poor with no recovery, seven digit negative numbers, negative zero bug and negative square roots all letting it down. Very similar in design to the Casio Memory-10

Components:	1 x cpu: Hitachi HD3691A 6A 31 (January 1976), 28 pin DIL 0.6" width 1 x 8 digit VFD; single tube round face E6535 2 x transistors 5 x diodes 9 x capacitors 6 x resistors 2 x resistor arrays 1 x transformer
Boards:	The keyboard assembly (B8H0E4C) is attached to the front with 6 screws. It links to the main cpu board (B8H-1A) via 12 strong copper wires. There is a small transformer board that piggy-backs on the main cpu board.
Construction:	Remove the screw from within the battery compartment and the back lifts off easily - hinge from the bottom as there are two lugs there.

Logic comments:	The (C) key is used to cancel an entry whilst the (AC) key clears the whole calculator
	Input overflow is suppressed inputting an ninth digit is ignored
	Negative numbers are shown with a "-” in the immediate left digit but as there is no ninth digit you are limited to seven digit negative numbers
	There is an selectable constant on all multiply and divide only by double-hitting the operator; i.e. (3)(X)(X)(=) gives "9", (=) gives "27"
	Negative square roots are allowed and result in a negative number
	Divide by zero shows “E” in the far right (first) digit and is not recoverable
	Overflow shows just “E” in the far right (first) digit and is not recoverable
	Memory storage is not indicated – you have to remember it and (AC) clears the memory too.
	This calculator has the "negative zero bug"; key in (0)(-)(1)(=) to give "-1" then (+1)(=) will give "-0"
	You can switch between full floating (F) and two digit round down notation