Sperry Remington 661-D

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Calculators: Handheld: Sperry Remington 661-D

		Size (approx):	80mm x 154mm x 40mm (max) (w,h,d) Weight 238g excluding batteries.
		Power:	6.0V DC, 4 x AA size batteries. Also accepts adapter (model AD-4145 500mW) through a top side socket on the left.
		Case:	Very solid square-shaped calculator made from smooth black plastic. Brushed aluminium panel covers half of the front. Display is tilted about 20 degrees with a neutral filter. Logo and model is printed on aluminium panel and has survived well. Keys are long travel, soft action and prone to double bounce after these many years. There is a tag on the left hand side (about 1cm down) for a carry strap which is not seen on this photo. Battery compartment has red pull-out silk tag. On/off switch is located on the left side about 3/4 of the way up. Front switch changes between zero and two fixed decimal points.
		Display:	6 digit blue VFD display - no seventh digit
		Features:	Basic four function
		Age:	1973
		Manufacturer:	Sperry Remington, a trademark of the Sperry Rand Corporation. Made in Japan. Serial No. (on battery cover) 567318.
		Comments:	Lovely early calculator with really shaky logic and operation. I probably would have thrown this calculator out of the window if I had bought it even though it feels like a dream! Lower segment zero display is typical quirky early Sperry. Case is dark brown leatherette with a full top and right side length zip. There is an embossed Sperry Remington logo on the front. These calculators are very similar to the early horizontal Casio machines like the Casio Mini CM602.

Components:	1 x cpu: Hitachi HD32154P 3G1, 28 pin DIL, 0.6" width (date code July 1973) 1 x IC NEC µPD129C X36095, 16 pin DIL, 0.3" width 6 x VFD tubes: NEC LD8035E 5 x transistors 5 x diodes 12 x capacitors 10 x resistors 2 x resistor arrays 1 x sealed transformer block
Boards:	The main cpu board (6E-1) sits loose and has the display and keyboard assembly mounted on it. Underneath is a secondary large board (6E-2B) which is joined by ten stiff wires. A piece of stiff sticky card separates the two boards.
Construction:	Remove the screw from the top edge. Then carefully prize apart one side (from the top) with a blunt soft instrument (I use wooden coffee stirrer sticks) to pop the lugs. Carefully hinge of the front of the case from the bottom edge. Quite difficult so if in doubt - don't risk damaging your calculator.

Logic comments:	The Clear key (C) will cancel last entry on the first press and clear the calculator on the second
	Overflow on the input of a number is suppressed
	There is no constant function
	The negative sign is shown on the immediate left but disappears past the sixth digit!
	Negative numbers are really dodgy - the "-" sign disappears when it feels like it!
	A divide by zero is flagged by "000000" an overflow error by "o" and is not recoverable
	The left arrow key is used to see the six least significant bits

	This is a close-up of the number "123045" in Sperry "small zero" notation. It has been suggested to me that this system was used as it was more capable of withstanding the failure of a particular display segment - and you could still tell what the number was.