Casio FX-31

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Calculators: Handheld: Casio FX-31

		Size (approx):	84mm x 145mm x 24.6mm (max) (w,h,d) Weight 132g excluding batteries.
		Power:	3.0V DC, 2 x AA size batteries, 0.25W. Also accepts adapter (AD-2S) through a socket on the top side to the far left. Battery life is quoted at 7 hours (manganese dry) and 24 hours (alkaline) continuous operation. The on/off switch is on the left hand side, just above the display.
		Case:	Smooth plastic white base and black top. Above the display is a full-width wrap around metallic sticker, in its own recess, printed black and blue with the brand and model number. A neutral and slightly tilted plastic display filter gives a clean image. The brushed aluminium keyboard surround is also recessed and printed black, blue and brown with key functions. Typical Casio keys are squishy but positive with individual plastic escutcheons.
		Display:	8 digit blue VFD with a ninth digit for negative indication and scientific mode display
		Features:	Four standard functions, square root, squares, change sign, reciprocal, factorial, pi, powers, nth root, trigs, stats, logs, sexagesimal conversion, sexagesimal display (DMS/HMS), DRG, six level parenthesis, three function memory. 6+2 scientific display mode.
		Age:	1978
		Manufacturer:	Casio Computer Co. Ltd., made in Japan. Serial number 0345985 on a sticker in the battery compartment.
		Comments:	Fabulous quality calculator from a famous range only missing fractions. As they got it so right, this layout remained for years - well into LCD calculators. Displays sexagesimal with a "°" symbol. Sound logic - but limited mantissa, basic memory and lack of error recovery. Original case is soft black plastic with open top and half-moon cut-outs either side. It has Casio embossed on the front and Made in Japan on the back. This calculator was branded as the Boots 425 which (from my example) is dated much later at 1981.

Components:	only bit not done 1 x cpu: Hitachi HD38111A 8F13 (date code June 1978) 28 pin DIL, 0.6" width black plastic 1 x 9 digit VFD display unit: single tube flat face: NEC FIP9D5 No.8G Japan 2 x transistors 11 x diodes 9 x capacitors 3 x resistors 1 x transformer TC-15 86 TDK
Boards:	Main board (Ref G8J-1B) is connected by 21 copper wires to the (and sits on top of the) keyboard board. The latter is secured to the front by 6 screws.
Construction:	Remove the two screws from inside battery compartment, and gently prize from the top pushing sideways to get the switch fully out. There is a strange (partial) keyboard layout embossed on the front case on the inside.

Logic comments:	The Clear key (C) is used to clear an input number, the all-clear (AC) to completely reset the calculator (which does not clear the memory).
	Overflow on the input of a number is suppressed, typing in a ninth digit is ignored
	The constant function is invoked for all four functions by a double press of the operator: i.e. (3)(X)(X)(4)(=) “12” (=) “36” etc.
	There is no indication of memory use - you have to remember it, and using the (Min) key will overwrite a previously stored number
	Negative numbers are shown with a “-“ to the immediate left of a number, travelling into the far left (ninth) digit to allow full eight digit negative numbers
	On overflow the display just shows "E" in the far right (first) digit and is not recoverable
	On divide by zero the display just shows "E" in the far right (first) digit and is not recoverable
	If you try to use more than 6 levels of parenthesis, or functions the display just shows “C” in the far right (first) digit and is not recoverable
	Negative square roots are not allowed and result in an error as above
	The change sign function can be used in mid number entry
	There is no recovery from any type of error
	There is a small exponent display bug: key in the number 12345678 then (EXP) which will display “123456 0.0” showing an erroneous decimal point in the exponent until you press equals
	You can enter degrees, minutes, seconds using the (° ' '') key, which it displays in decimal form. To see it in DMS form use the keys (INV)(<) when upper "°" symbols are used to separate the numbers.
	Some of the higher functions and all inverse functions are selected using a two key sequence starting with the (INV) key.
	Full ten digit precision is preserved try this; "1.01" then square root it until the answer reads "1" then (-)(1) to get 8.9 x 10^-8
	No major bugs found

Casio FX-31 manual

The manual measures approximately 130mm by 88mm and has 32 black and white pages in total. It is in English and Spanish and has loads of instructions and examples which are easy to locate and understand. Printed in Japan.