Casio Pocket Mini CP-801C

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Calculators: Handheld: Casio Pocket-mini (aka CP-801C)

		Size (approx):	60mm x 97mm x 21mm (w,h,d) Weight 74g excluding batteries
		Power:	3V DC, 2 x AA size batteries, 0.2W. It does not accept an adapter. The on/off switch is on the left side, at the top.
		Case:	Compact smooth two-piece black plastic calculator with full-cover aluminium inset on the front and half of the sides. Both end sections have a ridged design. Shaped a bit like a hip flask, the rounded corners make it nice to hold. The logo and name are silver printed raised letters on a raised display escutcheon. A neutral and flat display filter gives a clean very bright image. Typical Casio buttons, squishy but work positively.
		Display:	8 digit blue VFD with no ninth digit, small zero notation (see below)
		Features:	4 function calculator with percentages
		Age:	1975
		Manufacturer:	Casio Computer Company Ltd, Made in Japan. Serial number inside battery compartment and on the cover are missing in my example.
		Comments:	Compact palm-sized deign that still feels quite robust. The logic is weak with no recovery, basic memory, seven digit negative numbers and the negative zero bug. Still, cute though. The original case is soft black plastic with two top flaps and sturdy metal popper closing on the top edge. It has Casio embossed on the front and Made in Japan on the back. I have seen reference to a model CP-801B so there must have been at least three versions of this model.

Components:	1 x cpu: NEC PD973C H55276, 28 pin DIL, 0.6" width black plastic 1 x 8 digit VFD; single tube round face 8 x capacitors 2 x resistors 2 x resistor arrays 1 x transformer module; Fuji HPS 0610 5F-12 Pat No. 427559 (date code June 1975)
Boards:	The keyboard assembly (B8M-E4A) is fixed to the front with five screws. It is attached to the floating main cpu board (B8M-1A) via 13 strong wires.
Construction:	Remove the two screws from within the battery compartment. From the back gently pop the two lugs on the left side and then on the right. Do this by gently pushing in the front section. There is also a lug to pop in the battery compartment. The rear section will eventually lift away.

Logic comments:	The (C) button is used to clear last entry of a number and (AC) to clear the whole calculator
	Overflow on number input is suppressed, keying in a ninth digit is ignored
	An overflow error is flagged by a "E." in the far right (first) digit and is not recoverable
	Divide by zero results in a "E." in the far right (first) digit which is also not recoverable.
	There is automatic constant on all four functions
	Negative numbers are flagged by a "-" sign in the immediate left digit. As there is no ninth digit you are limited to seven digit negative numbers
	This calculator has the "negative zero bug"; key in (0)(-)(1)(=) to give "-1" then (+1)(=) will give "-0"
	It also has the divide to negative zero bug: key in (-)(1)(=)(/)(1)(0)(=)(=)(=) etc. to eventually get "-0"

		The tiny main board to the right has been bent back so you can see the attachment to the keyboard assembly. It measures just 54mm by 59mm and benefits from a Fuji transformer module to reduce the component count.
Note the unusual way that zero is represented - by only using the lower half of the digit. The main theory about this is that it allowed any particular segment to stop working and you could still identify the number.