Calfax 890P

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Calculators: Handheld: Calfax 890P

	Size (approx):	69-77mm x 140mm x 35mm (max) (w,h,d) Weight 104g excluding batteries
	Power:	9.0V DC using 1 x PP3 size battery. It accepts an adapter through a socket on the right hand side about half way up.
	Case:	Two piece matt black and white plastic case with an tapering shape and pronounced top section to accommodate the battery. On the top section there is a metallic sticker printed black with the brand and model number which sits in its own recess. A titled and slightly inset red plastic display filter gives a dull display with limited angle of view. The bold coloured proud keys are the short travel clicking type. The front section has white printed keyboard and switch labels.
	Display:	8 digit red LED display with bubble lens but no ninth digit.
	Features:	Standard four functions, percentages and selectable constant.
	Age:	1975, original price appears on the box sticker at $13.88 and a sticker in the battery compartment states 20 Jun 1975.
	Manufacturer:	No manufacturer's details, made in Hong Kong. Serial number on rear sticker is 247696. .
	Comments:	Solid and angular but generic looking calculator. The battery cover is big enough to get four AAs so it makes me suspect this was a general case that could fit many designs. Shaky logic with disappearing negative sign and decimal point bug but the recovery is good. I believe this calculator was not supplied with a cover – just a bubble-wrap bag.

Components:	1 x cpu: Rockwell A4130PA 7521 (week 21 of 1975) 42 pin DIL 1 x logic chip BD5025 7403 16 pin DIL 1 x nine digit flat LED display 20 x transistors 2 x diodes 17 x resistors 5 x capacitors 1 x transformer TP022
Boards:	Small cpu board is connected to the full sized keyboard and display board by 30-way ribbon cable. Board are secured using the case fixing screws.
Construction:	Remove the four screws on the back. Two of these screws are hidden underneath the sticky "model number" label. The case easily separates.

Logic comments:	(C/CE) is used to cancel the last number entered whilst a second press will clear the whole calculator.
	Input overflow is suppressed, inputting a ninth digit is ignored
	Negative numbers are shown with a minus in the digit to the immediate left but as there is no ninth digit to travel into you are limited to seven digit negative numbers. Or so you would think. It just disappears off the screen but is still there in the register thereby just allowing full eight digit negative numbers
	There is selectable constant on all four functions; to take three away from anything key in (3)(-)(K), then (7)(=) gives “4” and so on.
	Divide by zero shows zero and hangs the calculator which is recoverable using (C/CE)
	Overflow shows the result and hangs the calculator which is recoverable using (C/CE)
	The isolation the percentage key divides the current register by 100
	There is a psuedo-fixed decimal point “bug”. Try (0)(.)(0)(0)(+)(1)(=) to give “1.00” which remains when you do not exceed two decimal point answers.

	The box measures 95mm by 165mm and is 45mm deep. It is printed in black, red and green with a jazzy check pattern on the sides. Over-fitting lid and box construction is sturdy but only has sufficient room for the calculator. Made in Hong Kong and distributed by Calfax, Inc., 15 East 26^th Street, NYC, NY 10010, USA		The manual measures 76mm by 147mm and is printed in one colour, black only. Of the 14 pages only 9 are printed and one has perforations for the returnable guarantee “card” page. Basic instructions and examples are given. Printed in Hong Kong. Whilst the guarantee description says return to the US address if bought in the US, for the rest of the world it sates you should return it to RJP Electronics Ltd in Hong Kong. The guarantee card, however, has to be returned to Western Universal (H.K.) Ltd in Hong Kong. I guess one of these is the manufacturer.