Bowmar Math Mate II

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Calculators: Handheld: Bowmar Math Mate II

		Size (approx):	71mm(max) x 135mm x 25mm(max) (w x h x d) Weight 100g excluding battery.
		Power:	9.0V DC using 1 x PP3 size battery. It accepts an adapter (DC 9V undefined) through a socket on the right side half way up.
		Case:	Constructed from two pieces of white mottled plastic with rounded edges and corners. The oversized red plastic display filter gives a very bright image. It is raised, flat, and has raised lettering painted silver for the brand and model name. They keyboard surround is matt brown plastic with raised and silver painted lettering for the on/off switch and memory functions. The keys are short travel with a prominent click.
		Display:	8 digit flat red LED with a ninth for negative and overflow indicators.
		Features:	Standard four functions with percentages and four-function memory.
		Age:	1975 - my example came with a receipt from W. H. Smiths (a UK store) dated 28 October 1975
		Manufacturer:	Bowmar Consumer Products, Burlington, Ma 01803 USA, assembled in Mexico. Serial number 207941
		Comments:	Well made calculator at home in the hand or on the desk due to its wedge shape. This type of flat (multi-dot) LED display is better than the more common bubble lens type as the field of view is so much wider. The sister model "Math Mate" did not have the memory functions. The logic is quite sound with good recovery and useful memory functions, but let down by the pseudo fixed decimal and divide to zero bugs.

Components:	1 x cpu: Square spiral logo C-594 7449 (date code week 49 of 1974) , 28 pin DIL, 0.6" width black plastic 2 x IC: ITT 510-5N 7429 (date code week 29 of 1974) 1 x 9 digit flat LED display unit: Optostic with single linear lens 0 x transistors 1 x diode 0 x capacitors 10 x resistors 1 x transformer unit Astec AA1225A
Boards:	The main cpu board (PM908-409/B 5235) sits on top of the keyboard assembly (KB3145M5041 10651 OP401) and is held in place by two plastic posts. The boards are joined by a 14 pin connectors.
Construction:	Difficult to open so be careful not to damage your example. There are two lug slots at the lower rear that need to be pushed inwards and held there whilst you lever the bottom edge apart. The rear section will then lift off easily - slide it upwards.

Logic comments:	The (C/CE) key is used to clear the last number entered whilst a second press clears the whole calculator.
	Input overflow is suppressed, inputting a ninth digit is ignored
	There is automatic constant on all four functions
	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 zero and “C” in the far left (ninth) digit and is recoverable using (C/CE)
	Overflow shows the result and “C” (or “E” if negative) in the far left (ninth) digit and is recoverable using (C/CE)
	Memory use is by a two key sequence: to store in memory key in (M)(+) which is marked with "M+" to remind you.
	Memory exchange with the current display is operated by the (M<>X) key
	Memory overflow holds the resultant number
	It suffers the divide to negative zero bug: key in (-)(1)(/)(1)(0)(=)(=)(=) etc.. to eventually get "-0"
	It suffers the pseudo fixed decimal bug: key in (1)(+)(.)(0)(0)(0)(=) to give "1.000" which remains a fixed three digit number until more are required or you use multiply or divide

		The box measures approx. 136mm by 76mm and is 30mm deep so it's just big enough for the calculator and manual. It is a double tuck-end printed in black and half-tone red. There is a sticker with the model number, so I suspect this box also catered for the Math Mate (blue keyed model without the memory).. On the reverse side it proudly proclaims "Math Mate by Bowmar. The first inexpensive calculator good enough to be called Bowmar. Fully featured. Quick and easy to operate. Full one year guarantee." Printed in the USA, assembled in Mexico.
	The image left shows the main cpu board removed from the calculator. At the top you can see the single-lens Optostic LED display unit. At the very bottom you can see the row of metal pins that locate in the socket on the keyboard assembly. Bottom right is the blue and white Astec box, with transformer and built in components for voltage conversion. The two upper ICs (and row of resistors) are used to drive the display.		The manual measures 76mm by 128mm and is a 14 page fan-fold printed in black and red. Plenty of examples and basic instructions are given. My example came with an additional Purchase Registration card (to be mailed to Tucson, Arizona, USA. It also came with a Warrantee card, filled in from W.H. Smiths in Kent, UK. Bowmar's UK address is given as Portugal Road, Woking, Surrey, Tel Woking 68497.