Electronic Resources Memory Master

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Calculators: Handheld: Electronic Resources Memory Master

		Size (actual):	75mm x 153mm x 19mm (max) (w,h,d) Weight 122g excluding batteries
		Power:	4.5V DC using 3 x AA size batteries. It accepts an adaptor/charger (3.3-4.65V 350mW) through a socket on the top side to the far left. The on/off switch is on the left hand side just below the name plate. When the batteries are low an "L" is displayed in the far left (ninth) digit - thereby draining the power even quicker!
		Case:	Made from a two-piece matt black plastic case this calculator is quite a slim design. The top area is slightly thicker in order to accommodate the batteries. The top sectional has a metallic sticker printed with black text. The narrow red plastic display filter is flush and only slightly tilted but gives a clear display. The keyboard is surrounded by a brushed aluminium panel with black label keys. The concave keys are short travel, loud click type but work well on my example.
		Display:	8 digit red flat LED with a ninth digit for negative, low battery and error indicators. There is also a separate LED for memory indication to the far left of the display.
		Features:	Standard four functions with percentages and four function memory. Auto accumulate memory storage switch.
		Age:	1975
		Manufacturer:	No maker's name, no serial number, no model number. The manual is credited to Electronic Resources Ltd, Hong Kong.
		Comments:	Generic calculator that isn't too bad considering it has been made as cheaply as possible. I just cannot figure out why they would give you two cancel and recall memory keys! I also cannot understand why they would go to the expense of adding a separate LED for memory indication when they could have used the ninth digit. The logic is quite sound except for the fixed decimal bug. Original case is black soft plastic with flip over flap and front tuck in section.

Components:	1 x cpu: General Instruments C-595-1 7517 (week 17 of 1975), 28 pin DIL, 0.6" width 1 x 9 digit individual red display assembly with extra single LED and linear red magnifier 11 x transistors 0 x diodes 2 x capacitors 22 x resistors 1 x miniature potentiometer 1 x transformer
Boards:	The main board (740412D) is located on top of the keyboard assembly (ETCO E330A30) and mounted on four screws into plastic posts and sturdy metal straps.
Construction:	There is a screw underneath the Memory Master plate. To remove this would result in permanent damage - so don't bother. Fortunately I have a scrap example I obtained in a job lot of calculators for spare parts. With the screw removed you can pop the side lugs and eventually remove the rear of the case.

Logic comments:	(C/CE) cancels an incorrect numerical entry, pressing a second time clears the calculator
	Input overflow is suppressed, typing in nine digits ignores the ninth
	There is automatic constant on all four functions
	Negative numbers are shown by a minus in the immediate left digit travelling into the far left (ninth) digit thereby allowing full eight digit negative numbers.
	Divide by zero results in zero and an "C" in the far left (ninth) digit and is recoverable using (C/CE)
	Overflow shows the result with "C" (or "E" if negative) in the far left (ninth) digit and is recoverable using (C/CE)
	You can store an error state in the memory
	Memory store is indicated with a separate LED to the far left of the display
	The (RM/CM) key just appears to do exactly the same as the cancel memory (CM) and Recall Memory (RM) keys! You have to press this key twice to cancel the memory so it is not a "recall and cancel" key as one would first suspect.
	There is a switch labelled Sigma for automatic (or accumulation) memory. When this is set on every result of the "=" key is added to the memory.
	This calculator has the pseudo fixed decimal bug; key in (0)(.)(0)(0)(0)(+)(1)(=) and the answer will be "1.000". This fixed decimal mode remains for addition and subtraction until the result requires more precision.

	This scan of the main cpu board shows the on/off switch on a board to the top left. There is a green module board for the display consisting of nine flat LED seven segment units and one separate red LED. The linear red plastic filter/lens has been removed for this image. This filter lens has been crudely cut in width to fit within the case and - I found a spare filter fixing lug stuck inside this example! Lots of transistors and resistors but hardly any capacitors and no diodes. Odd square plastic encased transformer. The wire connectors you can see at the bottom go to the keyboard assembly.		The box measures 117mm by 167mm and is 32mm deep. It is printed in black and yellow and is of top/bottom tuck end construction. There is no country of origin or manufacturer or company name. It is quite a bit wider than the calculator so either something else was supplied (not enough room for an adaptor I would have thought) or there was a card inner former.
	The basic black and white manual measures 121mm by 67 mm and is 24 pages in total. Quite a good description and plenty of examples. Electronic Resources Ltd., Hong Kong.