National Semiconductor 853

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Calculators: Handheld: National Semiconductor 835

		Size (approx):	68mm (max) x 140mm x 22mm (max) (w,h,d) Weight 64g excluding batteries
		Power:	9.0V DC, 1xPP3 size battery. Also accepts adapter (undefined) through a socket on the left hand side, about mid way up.
		Case:	Rounded wedge-shaped case made from a two-piece matt brown plastic case. The red plastic display filter is inset and sculptured to form a tilted section. This gives a bright but limited viewing angle image. The keyboard surround is a textured plastic panel in cream and brown with reversed out text labels for the switch, keys, brand and model number. The small keys are short travel, rocking action, with a soft positive click.
		Display:	8 digit red LED with bubble lens and ninth digit for negative and memory indication
		Features:	Four function with percentages, square root and four function memory
		Age:	1977
		Manufacturer:	Made in Malaysia
		Comments:	Incredibly empty calculator for its age. This must have been one of the first "sealed chip on a board" designs - the only way calculators are made today. Quite poor logic as it has a lack of recovery, minus zero root bug and negative zero bug. See a similar design but quite different calculator in the 835A model.

Components:	1 x cpu: No ID 1 x 9 digit LED unit with individual bubble lens No other components
Boards:	Keyboard unit is attached to front of the calculator and fixed to the main board by 17 rigid wires. The very small main board mounts both the vulcanised sealed chip and display. There are no other components. Main Board has Nat Semi logo, Ref M381
Construction:	Remove the four screws on the back. The two piece case then separates easily.

Logic comments:	(CE/C) cancels an incorrect numerical entry, pressing a second time clears the calculator
	Input overflow is suppressed, keying in a ninth digit is ignored
	There is automatic constant on all functions
	Overflow shows the results with all decimal points alight and is not recoverable
	Divide by zero shows ".0.0.0.0.0.0.0.0." which is not recoverable
	Negative numbers are shown with a "-" to the immediate left of a number travelling into the far left (ninth) digit thereby allowing full eight digit negative numbers
	Negative square roots are allowed and result in a positive answer.
	Memory storage is flagged by one vertical segment in the far left (ninth) digit
	Used in isolation the percentage key will divide by 100
	It suffers the negative zero bug: key in (1)(-)(2)(=) to give "-1" then (+)(1)(=) will give "-0"
	This suffers the minus root bug: the square root of zero is -0 and continually toggles between zero and minus zero

			Small manual measuring 129mm x 65mm and is two colour (red and black) throughout. There are 24 additional printed pages. Covers the English, French and German languages. Is the generic manual for the 835, 850A. Only the 835 has square roots and memory and the 750 does not have percentages. Back states "(c) 1977 National Semiconductor P/N 102828. Printed in Hong Kong". There is also a smaller (118mm x 62mm) one colour blue, 8 page Warranty leaflet. Part No. 102832 also printed in Hong Kong,
The box is 70mm x 164mm x 28mm, not much bigger than the calculator. It is printed in black and brown which matches the calculator rather well.