Radio Shack EC-495

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Calculators: Handheld: Radio Shack EC-495

		Size (approx):	84mm x 155mm x 30mm(max) (w,h,d) Weight 166g excluding batteries
		Power:	6V DC using 4 x AA size batteries. It accepts an adapter (catalogue no. I4-854 or I4-9854)) through a socket on the top side in the middle. A note on the back warns that if you plan to use AC power for more than 2 hours, remove standard or alkaline batteries.
		Case:	Two-piece case made from glossy olive and dark brown plastic. The green plastic display filter is raised and tilted by the case shape to which it sits flush. It has the bran name printed in white text. The matching dark brown matt keyboard surround is printed with white text for the switch and higher-function key labels. The small keys are medium travel with a soft springy click on rebound.
		Display:	12 digit green VFD where the twelfth is used for negative, memory and error indication. Scientific mode of 5+2. Display is right reading and defaults to a rather odd 6 digit format.
		Features:	Standard four functions with trigs (including hyperbolic) and logs, sexagesimal conversion, Polar,/rectangular coordinates, square root, square, reciprocal, stats, factorial, powers, register exchange, pi, change sign, parentheses, three-function primary memory and six-function four-register memory. Scientific display mode.
		Age:	1978
		Manufacturer:	Tandy Corporation, made in Taiwan, serial number 069085, catalogue number 65-638A, reference 5A8.
		Comments:	Nicely built but a bit strange in its colour, function and display. Why default the display to a fixed five digit number with no trailing zero suppression - and then in scientific mode, only show five digit mantissas when all eight digits of precision are there and could be displayed? There appears to be an earlier(?) "4A8" numbered model which looks to be identical inside.

Components:	1 x cpu; Mitsubishi M58628-001P 7X3A (end of 1977 date code?), 28 pin DIL, 0.6" width black plastic 1 x 12 digit VFD single glass unit flat face: Futaba 12ST 22A 7H (August 1977 date code) 2 x transistors 17 x diodes 6 x capacitors 10 x resistors 2 x resistor array2 1 x transformer: Apollo CV-007
Boards:	The keyboard assembly (GICO CE-495 GK347-1 Japan M58-628-001P K1) sits loosely on top of the battery compartment and main cpu board and joined by 18 strong wires. The keyboard assembly has an additional date code sticker "53.3.24" which is 24th March 1978).
Construction:	Held together by internal lugs only - so be careful as damage can easily result. The best way I found was to lever off one of the front edges whilst gently squeezing in the back section. The front section will eventually lift off.

Logic comments:	This section is not complete as my sample has some keys not working - and I have no manual to refer to
	(C/CE) clears the last number entered on the first press and clears the whole calculator on the second
	It has a very odd display mode. It starts up with "0.0000" which retains its lack of trailing zero suppression with up to four digit decimal numbers but can go up to a full eight digits when required. Most scientific and higher functions only show five digits, even though the full nine digit precision is maintained in some. Try in degrees (5)(5)(COS) to show "0.5736" then subtract this number to get "-2.3663 x 10 ^-05". Cannot think of why it should do this instead of showing a full 8+2 scientific mode.
	Input overflow is suppressed, keying a ninth digit is ignored
	Negative numbers are shown with a minus in the far left (twelfth) digit thereby allowing full eight digit negative numbers
	There is automatic constant on all four functions
	Divide by zero shows "E0.0000" starting in the far left (twelfth) digit and is not recoverable
	Overflow shows "E0.0000" starting in the far left (twelfth) digit and is not recoverable
	Negative square roots are not allowed and show "E.0000" starting in the far left (twelfth) digit and is not recoverable
	Main memory store is indicated by the far left (twelfth) digit’s decimal point DONE TO HERE
	Memory overflow shows "E0.0000" starting in the far left (twelfth) digit and clears the memory
	Additional memories are accessed by the store (STO) and Recall (RCL) keys, to store five in memory-one key in (5)(STO)(1) and to recall it key in (RCL)(1). These memories are not indicated and I suspect the three/four memories are used in the statistical calculations
	The higher functions are access by pressing (F) first - which is indicated by the decimal point of the third digit and can be cancelled by keying (F) again
	This calculator suffers from divide to negative zero (once) bug: divide any negative number repeatedly and you will eventually get "-0.00000" then once more gives "0.00000"